3- Periodic Table, Physical Chemistry Flashcards
What is ionisation energy
The amount of energy required to remove one electron form each atom in one mole of gaseous atoms of an element to form one more of gaseous 1+ ions
Show first ionisation energy as a reaction
X(g) —> X+(g) +e-
Show second ionisation energy as a reaction
X+(g) —-> X2+ (g) + e-
What factors effect ionisation energy
The charge on the nucleus
The distance of the outer electrons from the nucleus
Amount of Sheila if created by the electrons between the outer electrons and the nucleus
How does the charge on the nuclus effect ionisation energy
More protons = more nuclear charge
More energy needed to remove an electron —> so a greater ionisation energy
How does the distance of the outer electrons from the nucleus effect ionisation we
Energy
Bigger distance - less attraction between electron and nucleus
Less energy needed to remove electron = smaller ionisation energy
How does the amount of shielding created by the electrons between the outer electrons and the nucleus effect ionisation energy
More energy levels = more sheliding
Less energy needed to remove an electron = smaller ionic energy
As you go down the group the energy required to remove an electron …….
And why
Decreases as it’s further from the nucleus and shielding by more electron
Generally as you go across a period the energy required to remove an electron ……..
Because..
Increases
As the electron you are removing is attracted more strongly by the nucleus because it has extra protons by t the distance + shielding have both remained the same (except a slight drop in atomic radius as you go across the period due to the increase in nuclear charge)
Do ionisation energy’s increase or decrease when there successive
Increases
Describe second ionisation energy
The energy required to remove one electron from each ion in one mole of gaseous 1+ ions of an element to form one more of gaseous 2+ ions
What does successive ionisation energy provide evidence for and how
the differnce energy levels
The jumps in ionisation energy
Why are there jumps in ionisation energy
Give an example
When you try to remove electrons from a lower quantum number there is a huge jump in ionisation energy
Eg. Sodium in group one
Removing one electron from 3s then it tried to remove one from 2p ( this is a huge increase in ionisation energy)
Ionisation energy generally increases as you go across the period .
What are the two exceptions
From group 2 to group 3
And
Form group 5 to group 6
Why is there a lower ionisation energy in group 3 than group 2
Group 3 is removing a p subshell
Group 2 is removing a s subshell
It’s easier to remove an electron from the p-subshell even though there is an extra proton increasing the attraction
This is because the 3s subshell is shielding the p-electron and the p-subshell is further away so less attraction
These factors override the effect of the increased nuclear charge resulting in the ionisation energy dropping slightly
Why is there a lower ionisation energy in group 6 than group 5
You have to start double fill in the orbitals in group 6
The repulsion between the 2 electrons in the same sub-orbital means that the electron is easier to remove so less energy is required
Is ionisation endothermic or exothermie and why
Endothermic - you have to put energy in to ionise an atom or a molecule
Is a lower ionisation energy easier to form an ion or harder
Easier
What does a high ionisation energy mean
There’s a strong attraction between the electron and the nucleus so more energy is needed to overcome the attraction and remove the electron
On a successive ionisation energy graph how can you tell which group an element is on
Count how many electrons are removed before the first big jump to find the group number
In the early 1800s, what were the only 2 ways to categorise elements
Physical and chemical properties
And by their relative atomic mass
When and by who attempted to group similar elements
1817
Johann döbereiner
What were the groups called in the 1817 on the periodic table
Döbereiner triad
How did johann döbereiner order the periodic table (why)
He saw that chlorine , bromine and iodine had similar characteristics
He also realised that other properties of bromine fell alfway between chlorine and iodine ,
He found other such groups of 3 elements (eg, lithium , sodium and potassium ) and called them triads
What and when did John newlands work on the periodic fable
And what did he call it
1863
He noticed that If arranged the events in order of mass, similar elements appeared at regular intivals - every 8th element was similar,
He called it law of octaves
He listed some known elements in rows od seven so that the similar elements lined up in columns
Why did John Newlands listing known elements in rows of 7 so that similar elemenys lined up in columns not work
The pattern broke down on the third row
With many transition elements like fe, cu, zn messing it up
Who created the first accepted periodic table amd when
Dmitri Mendeleev
1869
How did dmitri mendeleev order the periodic table
He arranged all the known elements by atomic mass, but left gaps in the table where the next element didn’t seem to fit
He could keep elements with similar chemical properties in the same group
He also predicted the properties of undiscovered elements that would go in the gaps
What showed Mendeleev was correct
When element were discovered with properti3d that matched Mendeleevs prediction and fit the gaps
Who and when produced the modern periodic table
Henry Moseley
1914
How did henery Moseley order elements
increasing atomic numbe
All elements within a period have the same …..
number of electron shells
Elements in a period have the same number of electron shells , what does this mean for trends
Repeating trends in physical and chemical properties across each perioid
This is known as periodicity
What is periodicity
Repeating trends in physical and chemical properties across each perioid
Elements in the same number of ….so,,,,
Electrons in their outer shells,
This means they have similar chemical properties
How can rhe periodic table be split up
S-block
D-block
P-block
f-block
What do ionisation energy prove exists
Shells
Is it an endothermic or exothermic reaction to ionise an atom or molecule
Endothermic
What is big jumps in ionisation energy show
New shells are broken into
(An electron is being removed from a shell closer to the nucleus)
What are diamond, graphite and graphene
Giant covalent lattices
What are giant covalent lattices
Huge network of covalently bonded atoms
What is another name for a giant covalent lattice
Macromolecules structure
Why can carbon atoms for giant covalent lattices
They can form 4 string covalent bonds
What are differnt forms of the same element inn the same state called
Allotropes
What are the allotropes of carbon you need to know
Diamond
Graphite
Graphene
How many covalent bonds are there in diamond for each carbon
4
What shape to atoms arrange themselves into in diamon d
Tetrahedral shape
It’s a crystal lattice structure
What is diamonds melting point
Very high
It sublimes Over 3800K
Properties of diamond
Very high melting point
Hard
good thermal conductor
Can’t conduct electricity
Won’t dissolve in any solvent
Why is diamond a good thermal conductor
Vibrations travel easily through the stuff lattice
Why cant diamond conduct electristy
Held in localised bonds
How many cobalent binds are in each silicon atoms in a crystal lattice
4
What element are the properties of silicon similar to
Carbon
Describe the structure of graphite
- the carbon atoms are arranged in sheets of flat hexagons covalently bonded with 3 each
- the sheets of hexagons are bonded together by weak London forces
- the 4th outer electron of each carbon atom is delocalised between sheets of hexagons
Why does graphite feel slippers
The weak London forces between layers in graphite are easily broken sot he sheets can slid over each other
What is graphite oftern used as and why
Dry lubricant and in pencils as slippery
Less dense - so is used to make strong lightweight sport equipment
Can graphite conduct electristy and why
The delocalised electrons in graphite arnt attached to any particular carbon atoms so are free to move along the sheets so an electric current can flow
Is graphite less dense than diamond + why
Yes
The layers are quite far apart compared to the length of the covalent bond , so graphite is less dense than diamond
does graphite have a high melting point + why
Strong covalent bonds in the hexagon sheets
Sumblimes ober 3900K
Is graphite soluble + why
No
The covalent bonds in the sheets are too strong to break
What is graphene
A sheet of carbon atoms joined together in hexagons
The Sheet is one atom thick, making a two dimensional compound
How many carbons is each carbon bonded to in graphene
3
Is graphene a good electrical conductor + why
Yes
The delocalised electrons in graphene are free to move along the sheet, without layers they can move quickly above and below the sheet
Is graphene strong + why
Yes
The delocalised electrons also strengthen the covalent bonds between the carbon atoms
What are the properties of graphene
Good electrical conductor
Strong
Transparent and light ( as only a single layer )
High melting point
Insoluble
Uses of graphene
High speed electronics
Aircraft’s technology
Touchscreens
What are the properties of graphene that give it the uses of Hugh speed electrons and aircraft technology
High strength
Low mass
Good electrical conductor
What are the properties of graphene that give it the uses of touchscreens
Flexibility
Transparency
What do metal elements exist as
Giant metallic lattice structures
Desicbe the structure and bonding if a giant metallic lattice structure
Rhe electrons in the outermost shell of metal atoms are delocalised
The electrons are free to move about the metal
This leaves a positive charged metal cations
The metal cations are elecrtostaticslly starched to the delocalised negative electrons, they form a lattice of closely packed cations in a sea of delocalised electrons,
What effects the melting point in giant metallic lattices
The number of delocalised electrons per atoms
The more there are the stronger the bonding will be and the higher the melting pinup
The size of the metal ions
The smaller ionic radius will hold the delocalised electrons closer the the nucleus
Why are metals malleable and ductile
There are no bond shielding specific ions together so the metal ions can slide past each other
Why are metals good thermal conductors
The delocalised electrons can pass kinetic energy to each others
Why are metals good electrical conductors
The delocalised electrons can move and carry a current
are metals soluble and why
No except in Liquid Metal’s
Becuase of the strength of metallic bonds
Properties of metals
Malleable
Ductile
Good thermal conductors
Good electrical conductors
Insoluble
Why are the simple molecular structures got a low melting and boiling point
The covalent bonds between the atoms in the molecule are very strong, but the melting and boiling points of simple molecular substances depend upon the strength of the induced dipole-dipole forces between their molecules. These intermolecular forces are weak and easily overcome, so these elements have low melting and boiling points.
Why is the melting point in S8 bigger than phosphorus or chlorine
Sulphur us a bigger molecule so stronger London forces
Why are the melting and boiling points in nobel gases very low
They exist as individual atoms
( so. Very weak London forces )
For period 2, how does the melting and boiling points change across the period
For metals They increase across the period because the metallic bond get stronger as the ionic radius decreases and the number of delocalised electrons increase
Then at giants covalent lattices they have strong covalent bonds Linking all the atoms tougher
A lot of energy is needed to break these bonds
Then at simple molecular structures, have only weak intermolecular forces to overcome between there molecules so they have low melting and boiling points
The noble gases have the lowest melting points as they are held togetehr by the weakest force
What charge ions do group 2 elements form
2+
How does ionisation energy change down group 2 and why
Ionisation energy decreases
Due to increasing atomic radius and sheliding effect
How do reactivity change down group 2 and why
When group 2 elements react they lose electrons, forming positive ions
The easier it is to lose electrons, the more reactive the element
So reactive increases Down the group
When group 2 elements react, are they oxidesed or reduces
And how do the oxidation states change
Oxidised
0 to +2
What do group 2 events react with water to produce
Metal Hydroxides + hydrogen
How does reactivity with water to produce hydroxides differ between elements in group 2
Be = doesn’t react
Mg = very slowly
Ca= steadily
Sr- fairly quickly
Ba - rapidly
What do group 2 elements burn in oxides to produce
Solid white oxides
What do group 2 elements produce when they react with dilute acid
Salt and hydrogen
What is the general trend for how vigorous a reaction gets with group 2 metals down the group
Increases down the group
The oxides and hydroxides of group 2 are …….., ………..in water and also ……….
Bases
Soluble
Alkalis
What do the oxides of group 2 metals react readily with water to form.
What kind of PH is the solution
+ what is the exception
Metal hydroxides
Which dissolve
Strongly alkaline
Magnesium oxide as only reacts slowly and the hydroxide isn’t very souble
Do the oxides form stoneger or weaker alkaline solution as you how down group 2 + why
Stringer
The hydroxides get more soluble
What is the name for group 2 elements
Alkaline earth metals
What are many of group 2 compounds used for
Neutralising acids
Uses of calcium hydroxide
Slakes lime
Used in agriculture to neutralise acidic soils
Uses of magnesium hydroxides and calcium carbonate
Used in some indigestion tables as antacids
Colour of florine
Pale yellow
Colour of chlorine
Green
Colour of bromine
Red-brown
Colour of iodine
Grey
What state is florine in at 20°c
Gas
What state is choline in at 20°c
Gas
What state is bromine in at 20°c
Liquid
What state is iodine in at 20°c
Solid
What do halogens exist as
Diatomic molecules
How does rhe boiling and melting point change down group 7 and why
Increases
Due to the increase if strength of London forces as the size and relative mass of the atom increases
How does volatile chmage down group 7
Decrease
What does it mean if a substance is said to be volatile
Said to have a low boiling point
What word should be used to describe a negative group 7 ion
Halide
How do halogens react
By gaining an electron to there outer shell,l forming 1- ions
Are Halogens reduced or oxidised
Reduced
Are holgens reducing agents or oxideisined agent +why
Oxidising agents as they oxidise another substance
How does atomic radii change down group 7
Increases
Why does reactivity decrease down group 7
As you go down the group, the atomic radi increase so the outer electrons are further fron The outer electrons are also shielded more from the attraction of the positive nucleus, because they are more inner electrons
This makes it harder for larger atoms to attract the electron needed to form an ion ( despite the increased charge on the nucleus), so larger atoms are less reactive.
What is another way of saying that halogens get less reactive down the group
They become less oxidising
Where can halogens relative oxidising strengths can be seen
In their displacement reactions with halide ions
How can u make changes easier to see when doing a displacement reaction with halide ions
Shaking with an organic solvent like hexane
The halogen that’s present will dissolve readily in the organic solvent, which settles out as a disticny layer about the aqueous solution
When will a halogen displace a halide form a solution
If the halide is below it in the periodic table
How to test form haldies
Add nitric acid to remove ions that might interfere with the test
Then add silver nitrate solution
A precipitate is formed
For the silver nitrate test for halide ions what colour will the precipitate be for chloride ions
White
For the silver nitrate test for halide ions what colour will the precipitate be for bromine ions
Cream
For the silver nitrate test for halide ions what colour will the precipitate be for iodine ion
Yellow
How can you back up your silver nitrate test for halides
By adding ammonia solution
Each silver halide has a differnt c9ublity in ammonia, the larger the ion is the more difficult it is to dissolve
What colour is chlorine water
Colourless
What colour is bromine water
Yellow
What colour is iodine solution
Orange / brown
What reaction takes places between KCl and chlorine water/ bromine water or iodine solution in either an aqueous solution or in organic solution
No reaction
What colour is KCl
Colourless
What colour is KBr
Coloureds
What colour is KI
Colourless
What colour is the reaction between KCl and choline water in an aqueous solution and in organic solution
Colourless
How many group are on the periodic table
18
Second ionisation energy
Energy required to remove one electron form each ion in on mole of gaseous 1+ ions of an element to from one mole of gaseous 2+ ions
Is second or first ionisation energy higher
Second
Units of ionisation energy
Kjmol-1
Do group 2 hydroxides become more soluble up or down the group
Down
All group 2 hydroxides when no soluble appear as a …..
White precipitate
Explain the observations of ca if excess h20 present
Effervescence
And solid ca dissapearing
Is. Magnesium hydroxides soluble or insoluble in water
Insoluble
Observation of magnesium hydroxides in water
A suspension of magnesium hydroxide in water
will appear slightly alkaline (PH9)
And some OH- ions must have been produces by a vert slight dissolving
What is calcium hydroxide classified as in term if solublitlity
Partially soluble I’m water
What is calcium hydroxides used in
Agriculture to neutralise acidic soils (slaked lime )
CaO- fuel gas desulfurisatuon
Limestone
What is magnesium hydroxide used in
Used as anti acids for treating acid indigestion
Milk of magnesia ( suspension of white mg2OH)
Use of barium sulphate
Barium meal (medical diagnostic tool)
Observation of magnesium in water
No reaction (very slow) with cold water
Burns with white foam to from a white powder wig steam
Observation if calcium and water
Fizzes in water and after time a white soils forms , which is slightly soluble in water
Observation of Sr in water
Fizzes in water and form a colourl3ss solution
Observation of barium in water
Fizzes in water and forms a colourless solution
A suspension of calcium hydroxide in water will appear what PH
Alkaline
11
Why does calcium hydroxide appear my alkaline in water than magnesium hydroxide
As it is more soluble so there will be more hydroxide ions present in solution
What is limewater made of
Calcium hydroxide
How to test fro co2
Lime water
Turns cloudy as where calcium carbonate is produced
Calcium oxide with water observations
Effervceseze
Solid ca disappeares
Solution forms
When solution becaime saturated and further metal ions - OH- will from, in a solid preciipitae
Does group 2 sulfate become less soluble up or down the group
Down
All group 2 sulfate when not soluble appear as what …..?
White precipitates
As group 2 becomes more reactive down the group
Fizzing (more vigorous down a group )
Metal disappearing (faster down the group )
Solution heating up ( greater temp change down the group)
What group 2 metal would would produce a white precipitate and why when reacted with water
Calsium
As it’s the least soluble hydroxide of these
Summarise the displacement reaction with halogens amd ions
Dissolve chlorine, bromine and iodine to prodice chlroine, bromine and iodine water
The use a poppet to drop i, Cl and br water onto a 3 by 3 grid
Then drop a drop of potassium choride solution in one of each halide water, then again with potassium bromide solution and potassium iodide
You can then observe which displacement reactions take place via a colour change
Chlorine amd bromine react with water so they appear what in water
Partially soluble
What does HClO act as
Bleach
Describe the trend in atomic radius down group 7
Atomic radius increases as you go down the group
Explain the increasing in atomic radius down group 7
In all of group 7 the outer electrons have a net pull of 7+ from the nucleus
Therefore the only factor effecting size of the atom is the number of layers of inner electrons
The more layers of electrons the more space they take up. Means atoms are to get bigger down the group
What is the trend in Electronegativity down group 7
Falls down the groups as the atoms become less good at attracting bonding pairs of electrons
Explain the decreasing in Electronegativity down group 7
The bonding pair of electrons feel the same net pull of 7 +. However for larger atoms down the group the bonding pair is further away from the nucleus so it won’t be as strongly attracted
Trends in melting and boiling point down group 7
Both melting and bp rise as you go down the group
Explain the trend in mp and bp down group 7
All halogens exist as diatomic molecules so IMF between molecules are London forces
As the molecule gets bigger, more e- which move around and set up temporary dipoles, which create attractions. The stronger London forces means more energy needed to melt/boil
What is bond enthalpy
The heat needed to break one mole of a covalent bond to produce individual atoms, starting form the origional substance in the gas state, and ending with gaseous atoms
What does bond ehtlapies in halogens depend on and what is the trend
Size of covalent bind attraction will depend on the distance form the bonding pair to tow nuclei
As all halogens - net pull of 7+ fro, both ends of the bond, so as the atom gets bigger bonding pairs get further from the nucleus so the strength of the bond falls.
Why is there an exception in bond enthalpys trend in F2
Because F-F atoms are so small it’s a very weak bind, as there are also 3 non binding pairs of electrons- as the bond is short the lone pairs get close enough to set up repulsion (weakening the bond)
When halogen atoms attach to a H atoms the effect of the F-F weakened bond doesn’t ahppen, why
There are no lone pairs on hydrogen atoms
What colour is fluorine gas
Pale yellow
What colour is chlorine gas
Green gas
What colour is bromine liquid
Orange
What colour is iodide solid
Black / grey
What state is fluorine in at rtmp
Gas
What state is chlorine in at rtmp
Gas
What state is bromine in at rtmp
Liquid
What state is iodine at rtmp
Solid
What colour is iodine gas ( and how does it become at gas)
Purple
Sublimes
What colour is bromine gas
Orange
What is the trend in oxidising ability down group 7
Decreasing down a group
T or f
Stronger oxidising agents take the place of weaker oxidising agents
T
What colour is the separated layer of chlorine when mixed with cyclohexane
Pale green
What colour is the separated layer of bromine when mixed with cyclohexane
Orange
What colour is the separated layer of iodine when mixed with cyclohexane
Purple
Is there a reaction between Bromine water and KCl in a aqueous solubtiom and organic solution
And what are the colours in each
No
aq - yellow
Organic - orange
Is there a reaction between iodine solution and KCl in a aqueous solubtiom and organic solution
And what are the colours in each
No
Aq- organe / brown
Organic - purple
Is there a reaction between chorine water and KBr in aqueous and organic solution + colours
Yes
Aq- yellow (br2)
Organic - orange (Br2)
Is there a reaction between bromine water and KBr in aqueous and organic solution + colours
No
Aq- yellow
Organic - orange
Is there a reaction between iodine solution and KBr in aqueous and organic solution + colours
No
Aq- orange / red
Organic - purple
Is there a reaction between choline water and KI in aqueous and organic solution + colours
Yes
Aq- orange / brown ( I2)
Organic - purple (I2)
Is there a reaction between bromine water and KI in aqueous and organic solution + colours
Yes
Aq- orange / brown (I2)
Organic - purple (I2)
Is there a reaction between iodine solution and KI in aqueous and organic solution + colours
No
Aq - orange / brown
Organic - purple
What is rhe symbol equation for chlorine with water
Cl2 + H2O -> HCL + HClO
Chlorine normally dissolves inc after to give what colour
Pale green
What is the name of HClO
Hypochlorous acid
Is chorine and water a reversbale reaction
Yes
If u add universal indicator is the products of chlorine and water what colour would it go
Red then HClO would bleach the colour
What is the name of NaClO
Sodium hypochlorate
What is the symbol equation of chlorine and dilute sodium hydroxide
Cl2 + NaOH —> NaCl + NaClO + H2O
How does the reducing power of halide ions change down the groupo and why
Increases as more deadly donates electrons as the outer electrons are further away from the nucleus and there is more shielding
Why does silver nitrate not work to test for fluorine
As silver floruide is soluble in water
Why is the silver nitrate test is it first acidified with diluiste nitiric acid
To remove any CO3 2- o4 OH_ ions present. Nitiric acid is chosen because we are using silver nitrate so NO3- ions won’t have an effect
If the colour isn’t obvious for the silver nitrate test for halide ions what can u do +what are the result s
Ammonia test
AgCl dissolves in dilute NH3
AgBr dissolves in conc NH3
Agl doesn’t dissolve
Halogens react with cold dilute alkali solutions In what type of reaction
Disproportionation
What is household bleach
NaClO
What is sodium chlorite (l) solution used in
Water treatment
To Bleach paper and textiles
Toilet cleaner
What are the products when chlorine mixes with water
And what type of reaction is thus
Hydrochloric acid and chloric (l) acid
Disproportionation
What is another name for chloric (l) acid
Hypochlorous acid
Aq chloric (l) acid ionises to make what
Chlorare (l) ions
What is another name for chlorate (l) ions
Hypochlorite
Why does added chlorine to water make it safe to drink
The product formed is chlorate (l) ions kill bacteria
What does chlorine do to make water safe
Kills disease causing microorganisms
Some chrloine remains in water and prevents re infection further down the supply
It prevents the growth of algae, eliminating bad tastes and smells and removes discolouration caused by organic compounds
How many people die each year due to waterborne disease such as …….
3.4 million
Eg. Cholera, typhoid, dysentery
Risks of chlorine to treat water
Chlorine gas is very harmful if breathed in - irritates respiratory system
Liquid chlorine on the skin or eyes causes severe chemical burns
Water contains a variety of organic compounds. Chlorine reacts with these compounds to form chlorinated hydrocarbons
And many of these are carcinogenic
what are the ethical considerations to chlorinated water
We don’t get a choice
Some people object to thus as forced ‘mass medication ‘
What could u use as an alternative to chlorine to clean water
Ozone
Uv
How does ozone (o3) clean water
+ negative
Strong oxidising agent which makes it great at killed microorganism
Expensive to protines and it’s short half life in water means that’s treatment isn’t permanent
How Does UV light clean water
+ negatives
kills microorganism by damaging their DNA
ineffective in cloudy water and it won’t stop the water being contaminated further down the line
How do u test for carbonates
Add dilute acid
If present then co2 will be released
Bubble through limewater - if co2 present limetwater turns cloudy ( as co2 forms a white precipitate of calcium carbonate)
Why do you use barium chrloide to test for sulfate
More sulfate are soluble in water but barium sulfate is insoluble so a precipitate will form
Explain the test for sulfate
Add dilute hcl
Then barium chloride solution
A white precipitate will form (barium sulfate)
What is the test for halides
Nitric acid
+ silver nitrate solution
Silver chloride - white precipitate
Silver bromide - cream precipitate
Silver iodide - yellow precipitate
If halide test is hard to see colour what further test can u do
Test solubility with ammonia
AgCl dissolves in dilute NH3
AgBr dissolves in Conc NH3
AgI is insoluble in NH3
why does the litmus paper need to be damp during the ammonia test
so the ammonia gas can dissolve and make the colour change
How to test if a substance contains ammonium ions
Add sodium hydroxide to your substance in a test tube and WARM the mixture. If ammonia is given off this means there are ammoniumions in your substanc
Ammonia gass is alkaline so to check use damp litmus paper- if present it will turn blue
What order do u do the ions test in
Carbonates
Sulfate
Halides
Describe the reaction between Cl- and br2
(No organic solvent used)
No reaction
Describe the reaction between Cl- and I2
(No organic solvent used)
No reaction
Describe the reaction between Br- and cl2
(No organic solvent used)
Yellow solution forms
What is the equation for cl2 + br -
Cl2 + 2br- —> 2cl- + br 2
Describe the reaction between br - and I2
(No organic solvent used)
No reaction
Describe the reaction between I-and cl2
(No organic solvent used)
Brown solution forms
Describe the reaction between I-and br2
(No organic solvent used)
Brown solution forms
Order the oxidising power of halides
Chlorine
Bromine
Iodine
Why does oxidising power decrease as you go down the group
Halogen atoms gain an electron when it oxidises the halide ion
The smaller the halogen atom the easier it is to gain an electron as it is smaller and less sheilding
Uses of chlorine
Kills bacteria ( used to treat drinking water)
Testies
Insecticides
20% of chlorine is used to make OVC. ( versatile plastic used in window frames, water pipes, electrial wiring insulation)
Oxidising agent
85% if pharmaceuticals use Charlie us or it’s compounds at some stage
Used as a chemical weapon in ww1
In the past used to make chloroform
What is the biological role of the choride ion
Mostly present in cell fluid as a negative ion to balence the positive (mainly potassiom) ions. Also present in extra cellular fluid. To valence positively ( mainly sodium ioms
We get most the chloride we need firm salt
What is the main mineral minned for chlorine
Halite
(Sodium chloride)
What happens when chlorine is added to water
+ how does this clean water
A Disproportionation reaction takes place,
Both products are acids - the bacteria is killed by chloric (l) acid and chlorate (l) ions
Why is barium chloride solution used to test for sulfate
Most sulfate are soluble in water but barium sulfate isn’t its very insoluble
What should u use instead of barium chloride if u are doing the haldie test after
Barium nitrate
( otherwise u are introducing chloride ions into the solution)
How should u alter the carbonate test I fu are testing for multiple ions in one iolution
Continue adding nitiric acid until bubbling tops so all the CO3 2- ions will have been removed
How should u alter the sulfate test if u are testing for a mixture of ions in one solution
Add an excess of barium nitrate
Any sulfate ions present will precipitate our as barium sulfate
Filter
Why is the order of anion tests important
CO3 2- must come first because you add dilute acid - you are looking for co2 gas. Niether sulfate of halides produce bubbles with dilute acid - so it can be carried out without the probability of an incorrect result
SO4- if u carried out the sulfate test on the carbonate you will. Get a white precipitate tooo so u need to carry out the carbonate test first
Halides - silver carbonate and silver sulfate are both inssoluble in water + will both form precipitates so u must do this test last
What is enthalpy change
delta H m is the heat energy transferred in a reaction at constant pressure. The unsure if deltas are KJ mol-1
What does deltaH O(with a line through and up small )
Shows that the measurements were made under standard conditions and that the elements were in their standard states (ie. Their physical states under standard conditions)
What are standard conditions
100kpa (about 1atm) pressure
298K (25°c)
Solution at 1mol dm -3
All substances should be in tori normal states at 298K
What is an exothermic reaction
Gives out energy
In exothermic reaction is delta H positive or negative
Negative
Is oxidation usually exothermic or endothermic
Exothermic
Guve 2 exampl3z of when oxidation is exothermic
Combustion of a fuel like methane (delta r H standard = -890 KJ mol-1 exothermic )
The oxidation of carbohydrates such as glucose in respiration
What is an endothermic reaction
Absorb energy
Delta H is positive
Give 2 examples of endothermic reactions
Thermal decomposition - of calcium carbonate is endothermic (delta r H standard = +178 Kj mol -1)
The main reactions in photosynthesis are also endothermic - sunlight provides the energy
What do enthalpy profile diagrams show you
How the enthalpy changed during reactions
What is activation energy
The minimum amount of energy needed to begin breaking reactant bonds and start a chemical reaction
In endothermic reactions are reactant or products more stable
Reactants
In exothermic reactions are reactants or products more stable
Products
The Delta H arrow should point which way for endothermic changes
Up
The Delta H arrow should point which way for exothermic changes
Down
What is the activation energy drawn between on an enthalpy profile diagram
Reactants and the top most point of the graph
The less enthalpy a substance has rhe ……… stable it is
More
What are the 2 ways to find enthalpy changes
Experiment
Data books
What are entahlpy changed you find in data books usually
Standard enthalpy changes
Why is it important to use standard conditions
Becuse changed in enthalpy are effected by temperature and pressure
Using standard conditions means that everyone can know exactly what the enthalpy is describing
What is standard enthalpy change if reaction
The enthalpy change when the reaction occurs in the molar quantities shown in the chemical equation under standard conditions with all reactants and products in their standard states
What is standard enthalpy change of formation
The enthalpy change when 1 mole of a compound is formed form its elements in this standard states, under standard conditions
What is standard enthalpy change of combustion
The enthalpy change when 1 mole of a substance is completely burned in oxygen under standard conditions with all reactants and products in their standard states
What is standard enthalpy change of neutralisation
The enthalpy change when an acid and a base react togetehr under standard conditions to form 1 mole of water with all reactants and products In their standard states
What is thermodynamics
Thermodynamics is the study of energy changes in a reaction, it allows us to look at stability of products and whether a reaction will occur or not.
What is a system
A system is the chemical or chemicals
being studied. If the system is closed there
is no exchange between the system and
the surroundings.
What is enthalpy change
An enthalpy change, ∆H, is the overall energy exchanged with the surroundings when a change happens at constant pressure and the final temperature is the same as the starting temperature. Units for ∆H are kjmol-1.
What are standard enthalpy changed
Standard enthalpy changes refer to reactions done under standard conditions, and with everything present in their standard states. Standard states are sometimes referred to as “reference states”.
Standard conditions are:
• 298 K (25°C)
• a pressure of 1 atm (100 kPa).
• where solutions are involved, a concentration of 1 mol dm-3
Exothermic example
Combustion
Respiration
Hot packs
Freezing
Endothermic examples
Melting and vaporisation
Photosynthesis
Why must energy be supplied to state a reaction
For a reaction to occur bonds must be broken and new ones formed
Units for actaivation energy
KJ mol -1
Activation energy definition
the minimum energy required to start a reaction by the breaking of bonds
Endothermic reaction definition
- a reaction in which the enthalpy of the products is greater than the enthalpy of the reactants, resulting in heat being taken in form the surroundings (delta H + ve)
enthalpy definition
the heat content that is stored in a chemical system
Exothermic reaction definition
a reaction in which the enthalpy of the products is smaller than the enthalpy of the reactants, resulting in heat loss to the surroundings ( delta H - ve)
What is the standard enthalpy change of formation of an element always
0
What is enthalpy
The measure of heat energy in a chemical system
Can you measure enthalpy
No but you can measure enthalpy change
How do you calculate enthalpy change
Enthalpy of products - enthalpy of reactants
What is enthalpy change of reaction
Heat given out or taken in as the reaction takes place
What is the enthalpy change equation
+ units
Energy (J) = mass of water (g) x specific heat capacity x temp change (c or K)
Energy (kj) / moles
How do u find temp change
T final - t inital
Is a rise in temp exo or endothermic
Exothermic
Is a drop in temp exo or endothermic
Endothermic
What is specific heat capacity of the surroundings
The energy required to raise the temperature of 1g of a substance by 1k
After an exothermic reaction calc, what do you add to the answer
- Infront of answer
After an endothermic reaction calc, what do you add to the answer
+
What is calorimetry
Substances are mixed in an insulated container
Scope for error of calorimetry
Loss of heat energy
Assumption that all substances have the same specific heat capacity of water
What about the specific heat capacity of the calorimeter
Slow or incomplete reaction
assumptions that density of suction = 1g/cm3
General calorimetric methord
washes the equipment (cup and pipettes etc) with the solutions to be used dry the cup after washing
put polystyrene cup in a beaker for insulation and support
Measure out desired volumes of solutions with volumetric pipettes and transfer to insulated cup
clamp thermometer into place making sure the thermometer bulb is immersed in solution measure the initial temperatures of the solution or both solutions if 2 are used. Do this every minute for 2-3 minutes
At minute 3 transfer second reagent to cup. If a solid reagent is used then add the solution to the cup first and then add the solid weighed out on a balance.
If using a solid reagent then use ‘before and after’ weighing method
stirs mixture (ensures that all of the solution is at the same temperature)
Record temperature every minute after addition for several minutes
In the calorimetric method if the reaction is slow than the exact temperature rise, can be difficult to obtain as cooling occurs simultaneously with reaction. How can you counteract this?
Take readings at regular time intervals and extrapolate the temperature curve line back to the time the reactants were added together and also take the temperature of the act a few minutes before they added together to get a better average temperature. If the two reactants are solutions and the temperature of both solutions need to be measured before addition and an average temperature is used.
Is bond breaking endo or exothermic
Eno
Is bond forming endo or exothermic
Exo
Stronger bonds take …….. energy to breaks
More
The amount of energy you need per mole to break bonds is called what
Bond dissociation enthalpy
Bond dissociation enthalpy always involve bond breaking in what type of compounds and why
Gaseous
To make comparisons fair
Water has two O-H bonds
Does it take the same amount of energy to break Both
And why
No
First is higher as OH- is easier to break apart because of extra electron repulsion
Why is the data book for O-H bond enthalpy bigger
It’s an average for a bigger range of molecules
What is the literature average bond enthalpy
The energy needed to break one mole of bonds in the gas phase, averaged over many differnt compounds
What do you need to know for the enthalpy change for a reaction
The number of moles of the stuff that is reaction
Change in temp
How do you find the enthakpy of combustion of a flammable liquid
Burn it
As fuel burns, it heats the water. You can work out the heat, absorbed by the water. If you know the mass of water and temperature change. 
What is specific heat capacity of water
4.18 J g-1 K-1
The enthalpy change accompanying a chemical change is independent of …..
The route by which the chemical changes occur
What is bond dissociation enthalpy
The amount of energy required to break one mole of a specific covalent bond in the gas phase
T or f
The magnitude of the energy required to break a specific bond is equal to energy to reform thus same bone
T
T or f
All covalent bonds require th same energy to break
F
How can energy required to break differnt covalent bonds be found
Experimentally from calorimetry
Data book values
Why are values of bond energy found experimentally for calorimetry differnt from data book values
Data book uses mean bond enthalpies
What is mean (average) bond enthalpy
Enthalpy needed to break one mole of covalent bond in a gaseous molecules, averaged over differnt molecules
Is mean bond enthalpy positive or negative
Why
Positive
As energy is required to break bond - only applied when substance starts and ends in gaseous state
What can actual bond enthalpy vary depending on
Chemical environment of the bond
What is Hess law
The total enthalpy change of a reaction is always the same, no matter which route is taken
Describe Hess law with an equation
Route 1 = route 2
In any chemical reaction energy is absorbed to ………….. and given out ……..
Break bonds
During bond formation
The differnce between the energy absorbed and released is the ………
Overall enthalpy change of reaction
A reaction won’t take place between two particles unless…..
And what is this called
1) they collide in the right direction, they need to be facing each other in the right way
2) they collide with at least a certain minimum amount of kinetic energy
Collision theory
What is activation energy
The minimum amount of kinetic energy particles need to react
(The particals need this much energy to break bonds to start the reaction )
Reactions with low activation energies happen easily or are moredifficult
Easily
How can you give particles energy
By heating them
Do new bonds need energy ot release energy
Release energy
On an energy profile diagram, whilst the graph is rising towards activation energy what is happening to the particles
The bond within each particle are being stretched
Molecules in a liquid or gas , do all the particles have the same kinetic energy
No
Some don’t have much and move slowly
Some have loads of kinetic energy and move quickly
Most are imbetween
If you plot a graph of the number molcules in a substance with differnt kinetic energies you get a ……
Boltzmann distribution
Describe Boltzmann distribution
- curve starts at (0,0) because no molecules have 0 energy
- then an increase as a few molecules are moving slowly
- the top part, most molecules are moving at a moderate speed so their energies are in this range
- then decrease, and anything after the activation energy line are the only molecules that have more energy than the activation energy, these are the only ones that can react
If you increase the temperature , what will happen to the particles on average
More kinetic energy and will move faster
So will collide more oftern ( tempt reaction is faster)
How will an increase in temperature effect the Boltzmann distribution curve
Greater proportion of molecules will have at least the activation energy and be able to react , this shifts the graph to the right
The origional Boltzmann distribution curve and an increased temperature curve will have what in common
The total number of molecules is the same which means the area under each curve must be the same
How does increasing concentration speed up reactions
If you increases the conc of reactants in a solution, the particles will be closer together, on average,
If they’re closer, they’ll collide more frequently
If there are more collisions they will have more chances to react
How does increasing pressure speed up reactions
if any of your reactants are gases, increases the pressure will increase the rate of reaction.
It’s pretty much the same as increasing conc of solution, at higher pressures, the particles will be closer together, increasing the chance of successful collisions
how does catalysts speed up reactants
Catalysts lower the activation energy by providing a differnt reaction pathway
If the activation energy is lower, more particles will have enough energy to react
Catalyst definition
A catalyst increases the rate of reaction by providing an alternative reaction pathway with a
Lower activation energy, the catalyst is chemically unchanged at the end of the reaction
Why do you only need a tiny bit of catalyst
They don’t get used up in reactions
They take part in reactions but they are remade at the end
Do all catalysts work on everything
No
Many will usually only work on a single reaction
What catalysts is used in the harbour process
Iron
How does activation energy change on an enthalpy profile diagram when a catalyst is added
it is lower
How does adding a catalyst effect the Boltzmann distribution curve
Activation energy line is lower
So more particles have the activation energy
What 2 categories can catalysts be split into
Heterogenous catalysts
Homogenous catalyst
What is a heterogenous catalysts
One that is in a differnt phase form the reactants
(Eg, in a differnt physical state for example the harbour process, gases are passed over a solid iron catalyst)
The reaction happens on the surface of the heterogenous catalyst. So increasing the surface area of the catalyst increases the number of molecules that can react at the same time , increasing the area of reaction
How does increasing surface of heterogenous catalyst effect the rate of reaction
The reaction happens on the surface of the heterogenous catalyst. So increasing the surface area of the catalyst increases the number of molecules that can react at the same time , increasing the area of reaction
What is a homogeneous catalysts
Homogeneous catalysts are in the same physical state as reactants
Usually a homogenous catalyst is an aqueous catalyst for a reaction between two aqueous solutions
How does a homogenous catalyst work
By forming an intermediate species, the reactants combine with the catalyst to make an intermediate species , which then reacts to form the product and reform the catalyst
Why do lots of industry’s rely on catalyst
They can lower the production costs, give more products in a shorter time and help make better products
(Eg, iron in ammonia production, if it wasn’t for the catalyst then temp would be raised loads to make reaction happen quick enough which would be expensive and reduced the amount of ammonia produced)
give an example of how using a catalysts can change the properties of a product to make it more useful
(Eg, poly(ethene) )
Made without a catalyst - less dence, lesss rigid
made with a catalyst - more dence, more rigid, higher melting point
How is using a catalyst sustainable
lower temps and pressures can be used to
So energy saves, less co2 released and fossil fuels reserves are preserved
Catalysts can also reduce waste by allowing differnt reactions to be used with a better atom economy
What are catalytic converters on cars made from
Alloys of platinum, palladium and rhodium
What do catalystic converters on cars do
They reduce the pollution released into the atmosphere by spreeding up the reaction,
2CO +2NO —> 2CO2 +N2
What are kinetics
Study of factors that effect the rate of chemical reactions
What is activation energy
Minimum energy needed to start a chemical reaction
What factors effect rate of reaction
Temp
Conc
Pressure
Sa
Catalysts
How does increasing temp effect rate
Increasing the temperature gives particles more kinetic energy. This makes particles move faster and with more energy, which means they are likely to have more frequent successful collisions if they encounter each other.
How does increasing concentration effect rate
Increasing the concentration increases the number of particles in a given volume which makes them more likely to encounter each other. This means there will be more frequent successful collisions.
How does increasing pressure affect rate
Increasing the pressure means the same number of particles are in a smaller space/volume. This means they are more likely to encounter each other and thus more frequent successful collisions
How does increasing surface area effect rate
Increasing the surface area causes there to be more surface for the particles to react on. This means they are more likely to come into contact with each other, meaning more frequent successful collisions.
What does a catalyst do
Provides an alternative route for the reaction with a lower activation energy
This means more particles are able to react, so a faster rate
Give some examples of reactions that happen every fast
Combining NaCl(aq) with AgNO3 (aq) produces a rapid precipitation forming AgCl (s)
Combustion of natural gas
A neutralisation reaction between an acid and an alkali
Hydrogen balloon ( barking dog reactions)
What does rate mean
Joe fast a reactant is used up or how fast a product is formed
What is rate of reaction
Change in conc. of reactants / products over time
What are the units for rate of reaction
Mol dm -3 s -1
What is Collision theory
Two reactant particles must collide for a recation to occur
Some collisions are effect while others are ineffective
What does they collision have to be to be effective
Particles collide with correct orientation
Participles have sufficient energy to overcome the activation energy barrier of the reactionn
How can you monitor rate of reaction
Monitor removal of reactants
Monitor formation of a product
- reactions where mass is lost
- recation that produce gas
- reactions where turbidity is measured
What is a catalyst
Increases rate of reaction by providing an alternative recation pathway with a lower activation energy.
They arnt used up so can be recovered chemically unchanged at the end of the reaction
What is most commonly used as catalysts
Transition metals
Or ‘valuable’ metals such as gold, platinum
What 2 ways can catalysts work
Can react with a reactant to form an intermediate
Or
Provide a surface for a reactopn to take place
What is a homogenous catalysts
Same physical state
Catalysts react with reactants to form an intermediate
Intermediate breaks down to give products
Give 2 examples of homogenous catalysts
H2SO4 catalysed
Alcohol + Carboxylic acid —> water + ester
Cl. Catlsyses
Ozone —> O2
What is a heterogenous catalyst (describe )
Differnt physical states to reactants
Usually solid in contact with gaseous reactants
Reactant molesculex are adsorbed onto surface where the reaction takes place
After the reaction , desorption of the product molecules occurs
What does adsorbed mean
Weakly bonded
What do catalytic converters do
Convert poisonous co, various nitrogen oxides in car exhausts into less harmful, co2 and N2
What is used in catalystic converters
Platinum
Palladium
Rhodium
(As the heterogenous catalyst )
How is the metal catalyst deposited in catalystic converted
Into thin layers onto a ceramic honeycomb, which maximises Sa and keeps amount of metal to a minimum
2CO + 2NO. —-> ……..?
Catalystic converter reacher
2CO2 + N2
When is nickle used as a catalyst
Hydrogenation
How are catalysts sustainable
Approximately 90% of all materials use a catalyst
Use of a catalyst enables lower temperature so reduces energy requirements, making it cheaper
It enables products to meet faster so increases profits
Catalyst increase rate, reduce waste products and energy consumption
What can happen to some catalysts so that they reduce in effectiveness
Can become ‘poisened’ by impurities
What do industries need to consider when making a sustaible process
High atom economy
Few pollutants
What is autocatalysts
A chemical reaction is said to have undergone autocatalysis if a reaction product acts as a catalyst for that reaction. Typically, the reaction starts slowly, and then speeds up as the products are formed. 
What does area under the maxwells blotzman distribution curve equal
The total number of molecules
What word can be used to describe the maxwells boltzman curve
Asymptotic
Why is the maxwell boltzman distribution curve asymptotic
Never touched x axis as that would mean giving a energy limit
Molecules in any gas are all moving at differnt ……
Velocities
How does a higher temperature effect the boltzman distribution curve
At higher temperatures, the peak of the curve is lower and moves to the right
The number of reactant molecules were very high energy increases
The total area under the curve is the same
A small increase in temperature can cause a large increase in rate of reaction due to the significant increase in the number of molecules with energy greater than the activation energy
How does increasing conc effect the maxwell boltzman distribution curve
If a concentration of the reactant molecules is increased, the curve retains the same basic shape, but the peak is higher higher. This indicates that there are more reactant molecules therefore greater area under the curve increasing concentration has a less significant effect on reaction and increasing temperature.
How does the presence of a catalyst affect the maxwell boltzman distribution code?
By providing an alternative route with lower activation energy, the amount of reactant molecules with energy greater than the new activation energy increases
What is the reactionary e
The rate at which a product is formed or a reactant is used up
Rate of recation equation
Amount of reactant used or product formed
———— ————————————————-
Time
How can you measure rate of reaction forms. Change in mass
+ advantage and disadvantages e
Change in mass
1) When the product is a gas, its formation can be measured using a mass balance.
2) The amount of product formed is the mass disappearing from the container.
3) When the reaction starts, you should start a stop clock or timer.
Then take mass measurements at regular time intervals.
4) Make a table with a column for ‘time’ and a column for ‘mass’ and fill it in as the reaction goes on.
5) You’ll know the reaction is finished when the reading on the mass balance stops decreasing.
6) This method is very accurate and easy to use but does release gas into the room, which could be dangerous if the gas is toxic or flammable.
How can you measure rate of reaction of a gas given off
+ advantage and disadvantage
Volume of gas given off
1) You can use a gas syringe to measure the volume of product formed.
2) The experiment is carried out the same way as above but you measure the volume of gas in the syringe rather than the mass from the balance.
3) This method is accurate but vigorous reactions can blow the plunger out of the syringe.
Except form change in mass and volume of gas given of
What other ways are there to measure amount of reactant used or product formed
Changed in pressure (for gases)
Changed in colour ( for solutions)
Changes in conductivity
How can you measure rate of reaction form a graph
The gradient (tangent)
How can reversible reactions reach equilibrium
2) As the reactants get used up, the forward reaction slows down — and as more product is formed, the reverse reaction speeds up.
31 After a while, the forward reaction will be going at exactly the same rate as the backward reaction so the amounts of reactants and products won’t be changing any more — it’ll seem like nothing’s happening
4) This is called dynamic equilibriume
What happens at dynamics equlibrium
. At equilibrium the concentrations of reactants and products stay constant
When can dynamic equilibrium only happen
In a closed system
What is a closed system
Nothing can get in or out
What principle predicts what will happen if conditions are changed at equilibrium
Le chatelier
What can alter the position of an equlibrium
Concentration
Pressure
Temeperature
If the equlibrium moves to the ……l you get more reactants
Left
If the position of equlibrium moves to the right you get more …
Products
If there is a change in conditions
The equilibrium will move to …… the change
Counteract
If you increase the conc of recants
What will happen with the equilibrium
The equilibrium tries to get rid of the extra reactant
It does ur by making more products so the equilibrium is shifted to the right
Decreasing the concentration has the opposite effect
If you increase the pressure what happens to the equilibrium
Shift the equilibrium to the side with the fewer gas molecules
Thus reduced the pressure
If you decrease the pressure what happens to the equilibrium
Shifts the equilibutm to the side with more gas molecules
This raises the pressure again
How does increasing tempertire effect equilibrium
Shifts in the endothermic (positive delta H) direction to absorb heat
How does decreasing tempertire effect equilibrium
Equilibrium shifts in the exothermic (negative delta Hl direction to try replace the heat
If the forward reaction is endothermic what will the reverse reaction be
Exothermic
How do catalysts effect the position of equilibrium
And why
They don’t
They speed up the forward and reverse reaction by the same amount
So they can’t increase yield, but they do mean equlibrium is reached faster
How is ethanol produced
And what are the conditions
Via a reversible exothermic reaction eg tween ethene and steam
60-70atmospheres, 300°c, phosphoric (v) catalyst
Why are conditions compromised in the formation of ethanol
I Because it’s an exothermic reaction, lower temperatures favour the forward reaction.
This means more ethene and steam are converted to ethanol at lower temperatures — you get a better yieid.
2 But lower temperatures mean a slower rate of reaction. So the 300 °C is a compromise between maximum yield and a faster reaction:
Higher pressures favour the forward reaction, so a pressure of 60-70 atmospheres is used — high pressure moves the reaction to the side with fewer molecules of gas.
Increasing the pressure also increases the rate of reaction.
But high pressures are expensive to produce, you need stronger pipes and container to withstand high pressures. In this process, increasing pressure also causes a side reaction to occur
So the 60-70 atmospheres is a compromise between maximum yield and expense
In the end it comes down to minimising costs
What do you need to work on the equilibrium constant
Homogenous reaction
Dynamic equilibrium
(Using conc of the products and reactants at equilibrium)
What is equilibrium constant written at
Kc
What is a homogeneous reaction
Where all the reactants and products are in the same physical state
What does Kc give you an idea of
How far to the left or right the equilibrium is
What is the expression for Kc
aA +bB ->(reverisble) dD + eE
Kc = [D]^d [E]^e
—- ————-
[A]^a [B]^b
The products go on the top line, the square brackets mean conc in mol dm-3
Lower case = the number of moles of each substance
How do you Calculate Kc
You can put the equilibrium conc into the expression
How can you estimate the position of equilibrium using the value of Kc
The larger, the value of KC, the further to the right, the equilibrium lies, and the more products there are relative to reactants
The smaller the value of Kc, the further to the left, the equilibrium lies , the more reactants there are relative to products
In a closed system the brown gas NO2 exists in equilibrium with …………….
What can this be used to investigate
Colourless gas N2O4
Effect of change in temp on equilibrium position
How can you use NO2 to investigate effect of changing temp on equilibrium position
Place two sealed tubes containing the equilibrium mixture in water baths — one in a
warm water bath and one in a cool water bath, and observe the colours of the mixure, The tube in the warm water bath will change to a darker brown colour as the
endothermic reaction speeds up to absorb the extra heat, pushing equilibrium to the let The tube in the cool water bath will lose colour as the exothermic reaction speeds up to try and replace the lost heat, pushing equilibrium to the right.
How do you investigate changing conc on position of equilibrium
Mixing iron (lll) nitrate (yellow) and potassium thiocyanate (colourles) results in a reversible reaction where the product is iron(Ill) thiocyanate (blood red). You end up with the following equilibrium…
Fe 3+ + 3SCN- —->< Fe(SCN)3
You can invest age what happens to the equilibrium position when the conc of products or reaction s are changed by monitoring the colour of solution
Methord:
1) take test tube 1 is the ‘control) and nothing is added to it, it keeps its initial reddish colour
2) add some iron (lll) nitrate to test tube 2, the mixture turns a deep red colour
3) add some post assist thiocyanate to test tube 3, the mixture is a deep red coooyr
4) add some iron (lll) thiocyanate to test tube 4. The mixture turned a yellow colour r
By adding more reactants the forwards reaction. Speeds up to produce more products (as seen by test tube 2 and 3) so equilibrium moves to right
By adding more productsm the reverse reaction speeds up to produce more reactants ( as seen by test tube 4) do equilibrium moves to the left
Equilibrium example
(Coppersulphate)
Which direction is endothermic
Hydrated copper sulphae =(revsible) anydoruse copper sulphate + water
Forwards
What is dynamic equilibrium
Forwards and backwards reaction occur at the same time (simultaneous
Y) and at the same rate
Concentrations become constant
What is the harber process equation
N2 (g) + 3H2 ==> 2NH3 (g)
What % of ammonia from the harber process is used to make fertilizersn
85%
What are the main 3 elements in fertilisers
NPK
Where does nitrogen for the harber process come from
The air
Where does hydrogen for the harber process come from
Reaction of methane with steam
What 3 things can you change to chnageb yield
Pressure
Temp
Conc
What 2 things do you need to check for, before changing pressure to alter yield
It only work if gases
Check number of moles on either side, same number will have no effectc
What is le chateliers principle
If a change is made to the conditions of a system at equilibrium. Then the position of equilibrium moves to the oppose that change in conditonsn
What happens to equlibrium in the harber process if we….
Increase N2
System opposes the change by
Shifting the position of equilibrium to the right in the forwards direction
This results in a greater yield og NH3
What happens to equlibrium in the harber process if we….
Decrease the temperature
The system opposes this change by
Shifting position of equilibrium to the right in the forward (exothermic) direction
This results in an increased yield of NH3
Why is compromised made on temperature in the harber process
What is the compromise
Lowering temp decrease rate
450°c
What happens to equlibrium in the harber process if we….
Increase the pressure
The system will oppose this change by
Shifting the position of equilibrium to the right which is the side with fewer moles
This results in an increase in tell of NH3
Condititin needed for an equilibrium
A closed system is isolated from its surroundings; temperature, pressure and concentrations are unaffected by outside influences.
The rate of the forward reaction is equal to the rate of the backward reaction.
The concentrations of reactants and products do not change.
How can you tell equilibrium has been reached on a conc to time graph
Plateos
When a system in equilibrium is subjected to an external change the system….
readjusts itself to minimise the effect of that change
When the position of equilibrium shifts to the left, it means the concentration of reactants
Increases
When the position of equilibrium shifts to the right, it means the concentration of products
Increases
What is homogenous equilibria
All equilibrium species are in the same state ( phase)
What is heterogenous equlibria
Species have differnt states (phases)
What is the reversible reaction of hydrated copper(ll) sulphate symbol equation
CuSO4.5H2O (s) = CuSO4(s) + 5 H2O(l)
What is the ammonium chloride decomposition symbol equation
NH4Cl (s) = NH3(g7 + HCl (g)
What is the equilibrium law
If the conc , of all substances present at equilibrium are raised to the power of the number of moles they appear in the equation, the product of the conc. of the roductx divided by the product of the conc, of the reactants is a constant.
Provided temp. Remains constant
What is used to represent conc
[]
What is the only thing that effects the value of Kc
Temp
What does the equilibrium constant tell you
The actual position of equilibrium
What does the magnitude of the quill room constant indicate
Whether there are more reacts of more products in an equilibrium system
What does rhe Kc value 1 indicate
A position of equlibrium that is halfway between reactants and products
What does the Kc value above 1 indicate
A position of equilibrium that is towards the products
What does the Kc value Bellow one indicate
A position of equilibrium that is towards the reactants
What are the units of Kc
Varies
It may not have any units
How do u do heterogenous equilibrium
When writing Kc expressions, omit any chemical substances that are solids or liquids, we only include aqueouse and gaseous chemical substances
This is because the conc. of solids and liquids are essentially constant
