Topic 3 - Periodic Table and Energy Flashcards
The relative mass of an electron
1/1836
The relative mass of a proton
1
The relative mass of a neutron
1
Charge of proton
+1
Charge of neutron
0
Charge of electron
-1
What is an isotope?
Isotopes are atoms of the same element, with a different number of neutrons (same number of protons/electrons)
In the periodic table, horizontal rows are called …
periods
In the periodic table, vertical collums are called …
groups
How many groups are there?
18
What is group 1?
Alkali metals
What is group 2?
Alkaline Earth Metals
What is groups 3-12/
Transition metals
What is group 15?
Pnictogens
What is group 16?
Chalcogens
What is group 17?
The halogens
What is group 18?
The noble gases
What are metalloids/semi metals? Why do they have that name?
Elements that touch the line between metal and non-metals, they have a combination of properties of metals and non-metals
Define ionisation
when an atom loses an electron from its outer shell.
Define first ionisation
The energy required to remove 1 mole of electrons from one mole of gaseous atoms of an element to form one mole of gaseous 1+ ions.
What 3 things can affect ionisation energy?
Shielding, nuclear charge and atomic radius
Define shielding
Shielding is when inner electrons screen the outer electrons from the pull from the nucleus
Define nuclear charge
The positive charge of the nucleus
Define atomic radius
Atomic radius is radius of an atom, we measure atomic radius by measuring the distance between 2 nuclei of touching atoms and halving the distance
Describe and explain the trend of atomic radius size as you go along period 3
There is an increase in nuclear charge as you go along the period. The stronger the nuclear charge the more it can pull the electrons closer to the nucleus. The shielding is the same as you go along the period. The general trend for atomic radius is it decreases as you go along period 3 as the electrons are pulled closer to the nucleus.
Describe and explain the trend of period 3 first ionisation energy
First ionisation energy enthalpy increases across a period, the nuclear charge increases across a period, attraction of electrons to the nucleus increases, atomic radius decreases (so electrons are closer), it takes more energy to remove that first electron.
Why does first ionisation energy dip between magnesium and aluminium?
There is a decease between magnesium and aluminium as magnesium has a full sub-shell stability, as the highest occupied sub-shell is complete (3s). Aluminium has one electron in a higher sub-shell (3p), this one electron is removed more easily as it is further away from the nucleus, and therefore the first ionisation energy is lower than magnesium.
Why does first ionisation energy dip between phosphorus and sulphur?
There is a decrease between phosphorus and sulphur because phosphorus has a half subshell stability, sulphur has one 3p orbital that contains a pair of electrons. These paired electrons repel each other, so one of these electrons is easier to remove therefore sulphur has a lower fist ionisation energy then phosphorus.
Describe and explain the trend in first ionisation energy as you go down group 3
First ionisation energy decreases down a group.
This is because more inner shell electrons as you go down the group, so there is shielding of outer electrons, attraction of electrons to the nucleus decreases, atomic radius increases (so electrons are further away).
Where does metallic bonding occur?
Only in metals
Describe and explain the metallic structure
.Giant structure
.The atoms are in tightly packed layers, which form a regular lattice structure
.Each atom in a solid metal structure has donated its negative electrons from its outer shell forming an ion
.The outer electrons become delocalised and create a ‘sea of free electrons’
.The positive metal ion (cation) is fixed in a portion maintaining the structure of the metal
.The delocalised electrons are mobile and can move through the structure
Define metallic bonding
.Metallic bonding is the strong electrostatic attraction between the metal ions (cations) and the delocalised electrons
Where do metals conduct? Why?
.Most only conduct in solid and liquid states
.The delocalised electrons can move freely anywhere with the metal lattice allowing them to conduct electricity
Why do metals have large bp/mp?
.Strong electrostatic attraction between the metal ion and the delocalised electrons
.Needs a lot of energy to break
What does the strength of the metal depend on? What does this also affect?
.The strength of metal depends on the charge of the metal ion in the structure (the greater the charge, the greater the number of delocalized electrons, the stronger the attraction, the stronger the bond)
.This also affects the size of the ion (the smaller the ion, the closer the electrons to the nucleus, the stronger the bond)
Do metals dissolve in solvents?
no
Why are metals good conductors of heat?
.When a metal is heated the delocalised electrons gain kinetic energy and move faster
.This movement transfers the gained energy throughout the metal
Why are pure metals soft?
When a metal is hit, the layers of metal ions are able to slide over each other, and so the layers do not shatter
What is an alloy and why are they harder than pure metals?
.An alloy is a mixture of two metals, thereby distorting the layers so they can’t slide over each other and make a harder new metal
diamond structure
.Giant covalent bonding .Forms a lattice .Made of carbon only .Strong covalent bond between each atom .Each carbon is bonded to 4 other carbons
Diamond properties
.Hard – a giant covalent structure and has lots of strong bonds
.Doesn’t conduct electricity – no delocalised electrons that can move
.High melting point – many strong covalent bonds between atoms , it needs a lot of energy to break
Graphite structure
.Giant covalent bonding
.Made of carbon only
.Hexagonal structure
.Strong covalent bonds between carbon atoms
.In parallel layers
.Weak intermolecular forces between layers
.Each carbon is bonded to 3 other carbons
.Delocalised electrons in each layer
Graphite properties
.Soft/slippery – the layers can slide over each other because there are weak forces between the layers
.Conduct electricity – delocalised electrons that can move through the whole structure
.High melting point – graphite has a giant structure with lots of strong covalent bonds between atoms, it needs lots of energy to break bonds
What is graphene? properties
.One layer of graphite
.Highly conductive and strong and flexible
What is a nanotube?
When graphene forms a tube like strutcure
What is a bucky ball?
When carbon forms a cage like structure
What are different physical forms of elements called?
allotropes
On a melting point across a period graph, how can you section the different points?
Metallic bonding, giant covalent structures, covalent molecules
Why does the melting point increase across period 3?
.The charge in the metal ions increase
.The number of delocalised electrons increases
.So the strength of the metallic bonding increases
.Need more energy to break stronger metallic bonds so the melting points and boiling points increase
Is silicon a metal or non-metal?
TRICK QUESTION
Its a metalloid
What is silicons structure like?
It has a giant covalent structure exactly the same as carbon in diamond (each silicon is bonded to four other silicon’s)
Why does silicon have a high melting point?
you have to break lots of string covalent bonds in order to melt it, and this requires a lot of energy to break.
How do phosphorus, sulphur and chlorine exist?
simple molecules, with strong covalent bonds between their atoms.
How does argon exist?
Argon exists as separate atoms (it is monatomic)
Why is Cl, Ar, S8 and P4’s melting points so low?
- When these four substances melt or boil, it is the London forces between the molecules which are broken. These are very weak bonds. So little energy is needed to overcome them.
In what order do the melting points of Cl2, Ar, S8 and P4 decrease? Why?
The strength of the intermolecular forces increases with the number of electrons, so the melting point decreases in this order:
S8 > P4 > Cl2 > Ar
What happens to the size of the metal atoms down group 2?
increases
What happens to the shielding of the outer electrons down group 2?
Increases
Describe and explain reactivity down group 2?
.Reactivity increases down group 2
.The size of the metal atoms increases down group 2
.The shielding of the outer electrons increases
.The outer electrons require less energy to remove as the attraction to the nucleus is less
.Meaning the metal is more reactive
What happens to oxides of group 2 elements when they react with water?
they release hydroxide ions and make a metal hydroxide.
CaO(s) + H2O(l)
Ca(OH)2(aq)
Why does alkalinity increase down group 2?
the metal hydroxides are more soluble
What happens when metal hydroxides react with water?
they make a white precipitate, which will dissolve into the water
Uses of group 2 compounds
to treat indigestion, agriculture and medicine
Uses of group 2 compounds in indegestion
e.g. Gaviscon and Rennies are made with calcium carbonate
Milk of Magnesia with magnesium hydroxide
Use of group 2 compounds in agriculture
in fields you get soil that has acidic conditions
treat the soil with an alkali, usually calcium hydroxide (lime)
Use of group 2 compounds in medicine
Barium meal made of barium sulphate, which is completely insoluble in water
What are halogens elemental forms like?
Diatomic molecules
What are halides?
Halogen ions with charge -1
What are halides like?
Monoatomic ions with full outer shells
F appearance at room temp
Pale yellow gas
Cl appearance at room temp
Pale green gas
Br appearance at room temp
Orange liquid
I appearance at room temp
Grey solid
Br appearance of vapour
Orange gas
I appearance of vapour
Purple gas
Trend in group 7 reactivity
lower as go down group
Describe and explain halogen boiling points
Halogen molecules increase in size as we go down the group, this leads to greater London forces between molecules, increasing the energy needed to separate the molecules and therefore higher melting and boiling points.
Fluorine boiling point
-118’C
Iodine boiling point
184’C
Describe and explain electronegativity trend in halogens
Electronegativity of the halogens decreases down the group due to an increase in atomic radius.
Increased nuclear charge is outweighed because there are more electron shells and more shielding. Iodine atoms therefore attract electron density in a covalent bond less strongly than fluorine.
Describe electron configuration in halogens
7 electrons in the outer shell, highest energy electrons in a p sub-shell
Each element has one fewer electrons than the next noble gas
Outer p subshell containing 5 electrons (needs one more to form a -1 ion)
Halogens are a strong oxidising agent, what does this mean?
They gain electrons
Why does reactivitity/oxidising power decrease down the halogens group?
.Atomic radius increases
.Electron shielding increases
.Ability to gain an electron decreases
Cl in water and cyclohexane
Pale green
Br in water and cyclohexane
Orange
I in water
Brown
I in cyclohexane
Violet
What is cyclohexane?
An organic solvent
Sodium chloride and chlorine water colour change, and with organic solvent (cyclohexane)
Stayed clear
Pale green
Sodium bromide and chlorine water colour change, and with organic solvent (cyclohexane)
Clear to pale yellow Reddy brown
Sodium iodine and chlorine water colour change, and with organic solvent (cyclohexane)
Clear to reddy brown Violet
Sodium chloride and bromine water colour change, and with organic solvent (cyclohexane)
Clear to pale yellow Orangey brown
Sodium bromide and bromine water colour change, and with organic solvent (cyclohexane)
Clear to pale yellow Orangey brown
Sodium iodide and bromine water colour change, and with organic solvent (cyclohexane)
Clear to reddy brown Violet
Sodium chloride and iodine water colour change, and with organic solvent (cyclohexane)
Clear to pale brown Violet
Sodium bromide and iodine water colour change, and with organic solvent (cyclohexane)
Clear to pale brown Violet
Sodium iodide and iodine water colour change, and with organic solvent (cyclohexane)
Clear to pale brown Violet
In displacement reactions between halogens and halides, what acts as an oxidising agent?
The halogen
If the halogen is an oxidising agent, what does this mean?
.Oxidises the halide ion to the halogen
.Gains electrons
.Is reduced to form the halide ion
Halogen oxidising ability order
BOTTOM I, Br, Cl, F TOP
What does chlorine dissolve in water to form?
an acidic solution of hydrochloric acid and chloric (I) acid.
chloric(I) acid formula
HOCl
How is water and chlorine a disproportionation reaction?
chlorine is both oxidised and reduced, from 0 to -1 in HCl and from 0 to +1 in HOCl
What does chlorine react with cold dilute sodium hydroxide to form?
sodium chlorate (I) and sodium chloride and water
sodium chlorate (I) formula
NaOCl
How is chlorine and cold dilute sodium hydroxide a disproportionation reaction?
chlorine is both oxidised and reduced, from 0 to -1 in NaCl and from 0 to +1 in NaOCl
Why is chlorine used to purify water samples?
because it is toxic to bacteria, some of which may cause disease
What is the risk of using chlorine to purify water samples?
chlorine is also toxic to humans, so there are risks associated with gas leaks during the chlorination process. There is also a risk of the formation of chlorinated hydrocarbons, which are also toxic
Why does the chlorination of drinking water raise ethical questions?
raises questions about individual freedom because it makes it difficult for individuals to opt out.
What does household bleach commonly contain?
the chlorate(I) ion in the form of sodium chlorate(I), NaOCl.
What does the chlorate(I) ion act as, what does it do?
It oxidises the organic compounds in food stains, bacteria and dyes.
Test for carbonate ions
- Add dilute nitric acid to the solid or solution
- Bubble any gas made into limewater
- If ions present the lime water will turn milky
Test for sulphate ions
- Add dilute hydrochloric acid
- Followed by aqueous barium chloride solution
- You will see a white precipitate being formed if sulphate ions were present as BaSO4 is made
Sulphate ions test ionic equation
Ba2+ + SO42- BaSO4
Halide ions test
- Add dilute nitric acid
2. Followed by aqueous silver nitrate solution
Why, in the halide ions test, do you have to use nitric acid?
since chloride is present in HCl
Colour of precipitate for Cl- anion
White
Colour of precipitate for Br- anion
Cream
Colour of precipitate for I- anion
Yellow
What do you do if you can’t tell the difference after the halide ion test?
you then add aqueous ammonia (NH3).
What does aqueous ammonia do to the different halide anions, why?
Chloride ions are soluble and the precipitate redissolves.
Bromide ions are soluble and the precipitate redissolves.
Iodide ions are insoluble so the precipitate will stay.
Sequence of anion tests
CaSH = Carbonate, sulphate then halides
Ammonium ion test
- Add aqueous sodium hydroxide
- Gently warm
- Hold moist pH paper above, turns blue
What contains enthalpy?
Elements and compounds
What is enthalphy (H)?
the heat that is stored in a chemical system
What is a chemical system?
The system refers to the atoms, molecules and ions making up the chemicals
Enthalpy cannot be measured, what can?
Enthalpy change
What is enthalpy change (ΔH)?
the difference in enthalpy between the products and reactants in a reaction
What happens in an exothermic reaction?
.In an exothermic chemical reaction heat energy is transferred from the system to the surroundings
.Any energy loss by the system is balanced by the energy gain by the surroundings
.The temperature of the surroundings increases, so we see a temperature increase
What happens in an endothermic reaction?
.In an endothermic chemical reaction heat energy is absorbed from the surroundings into the system
.Any energy gain by the system is balanced by the energy loss of the surroundings
.The temperature of the surroundings decreases, so we see a temperature decrease
Burning fuel, exo or endo?
Exo
Condensing a vapour, exo or endo?
Exo
Evaporation, exo or endo?
Endo
Neutralising an acid, exo or endo?
Exo
Thermal decomposition of copper carbonate, exo or endo?
Endo
Rapid oxidation of iron, exo or endo?
Endo
Shop bought hand warmers, exo or endo?
Exo
Sports injury cool packs, exo or endo?
Endo
Enthalpy change equation
H(Products) – H(Reactants)
Sign for exothermic reaction
negative
Sign for endothermic reaction
positive
Define activation energy
The minimum amount of energy required to start a reaction by breaking the bonds
Draw an exothermic activation energy graph
Check notes
Draw an endothermic activation energy graph
Check notes
Draw an exothermic enthalpy profile
Check notes
Draw an endothermic enthalpy profile
Check notes
Define Enthalpy change of reaction (ΔHr) with example
the enthalpy change when the reaction occurs in the molar quantities shown in the chemical reaction
e.g. Zn(s) + Cu2+(aq) Cu(s) + Zn2+(aq)
Define Enthalpy change of formation (ΔHf) with example
the enthalpy change when 1 mole of compound is formed from its elements
e.g. C(s) + O2(g) CO2(g)
Define combustion change of reaction (ΔHc) with example
the enthalpy change when 1 mole of substance is burnt
e.g. CH4(g) + O2(g) CO2(g) + H2O(g)
Define Enthalpy change of neutrilisation (ΔHneut) with example
the enthalpy change when solutions of an acid and an alkali react together under standard conditions to produce 1 mole of water. It is always measured per mole of water formed.
e.g. HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)
What symbol is used for standard conditions?
ϴ
What conditions are used for enthalpy change values?
Standard conditions:
Standard pressure = 100KPa
Standard temperature = 298K (25’C)
Standard concentration = 1 moldm-3
Two equations for calculating enthalpy changes
q = mcΔT ΔH = q/n
What is each part of ΔH = q/n?
q = heat energy (J) n = number of moles (mol)
What is each part of q = mcΔT?
q = heat energy (J) m = mass of substance heated or cooled (g) c = specific heat capacity of water (4.18 Jg-1K-1) ΔT = change in temperature (‘C or K)
What is the final step of calculating enthalpy change equations?
Multiply the answer by the co-efficient of the reagent not in excess
When doing enthalpy change calculations, and you dont have a weight for the solution, what do you use?
The volume of it in cm^3, Cm^3 = g
When doing enthalpy change calculations with an equation and bond energy values, how do you get the final answer after finding the values of either side of the equation?
bonds broken - bonds made
left - right
Define average bond enthalpy
the average enthalpy change when one mole of gaseous covalent bonds is broken
Why might the calculated average bond enthalpy different from the actual?
.The bond enthalpies used in the calculations are averages from different compounds, the exact bond enthalpy depends on the particular compound in which it is either formed or broken
.The bond enthalpies are not determined under standard conditions. Bond enthalpies are determined by molecules in a gaseous state. But at 298K not all compounds are a gas, such as water.
In terms of enthalpy, what is breaking of bonds always? Why?
Always endothermic, as you need to add energy to break bonds
What can average bond enthalpy also be called?
Mean bond enthalpy
Where is average bond enthalpy taken from?
the average is taken over a wide range of compounds containing that type of bond
State the standard conditions
Standard pressure = 100kPa (1 atmosphere)
Standard temperature = 298K (25’C)
Standard concentration = 1moldm-3
Standard states of all substances (carbons is a solid, hydrogen is a gas and water is a liquid)
Define standard enthalpy change of reaction
The enthalpy change for a reaction as shown by the molar quantities in the chemical equations
Measured under standard conditions
Define standard enthalpy change of combustion
Enthalpy change when 1 mole of a substance reacts completely with oxygen under standard conditions`
Define standard enthalpy change of formation
The enthalpy change when 1 moles of substance is formed from its elements under standard conditions
Enthalpy change of formation of elements is always …
zero
What to remember for Hess’ Law Cycles Involving Enthalpies of Formation
Using delta H f it’s p-r!
Formula for hess’ law cycles involving enthalpies of formation
sum of ΔHf products - sum of ΔHf reactants
Why does oxygen have no enthalpy of combustion value?
Oxygen can’t be combusted
What does Hess’ law state?
Hess’ law states that the overall enthalpy change of the two routes is the same
Equation for Hess’ Law Cycles involving enthalpies of combustion
sum of enthalpy of combustion of reactants - sum of enthalpy of combustion of products
Does breaking bonds require or release energy?
Require
Does forming bonds require or release energy?
Release
Define exothermic
the energy required to break bonds is less than the energy given out when new bonds form
Define endothermic
the energy required to break bonds is more than the energy given out when new bonds form
Define average bond enthalpy
the average enthalpy change when one mole of gaseous covalent bonds is broken
Equation for enthalpy change
enthalpy of bonds broken – enthalpy of bonds formed
Why might calculated bond enthalpies not be right?
- The bond enthalpies used in the calculations are averages from different compounds, the exact bond enthalpy depends on the particular compound in which it is either formed or broken
- The bond enthalpies are not determined under standard conditions. Bond enthalpies are determined by molecules in a gaseous state. But at 298K not all compounds are a gas, such as water
Draw a general diagram for Hess’ law
CHECK NOTES
Enthalpy change of reaction –
This is the enthalpy change when the reaction occurs in the molar quantities shown in the chemical equation
Enthalpy change of formation –
This is the enthalpy change when 1 mole of compound is formed from its elements
Enthalpy change of combustion –
This is the enthalpy change when 1 mole of substance is burned
Enthalpy change of neutralisation –
The enthalpy change when solutions of an acid and an alkali react together under standard conditions to produce 1 mole of water. It is always measured per mole of water formed.
Hess’ Law
If a reaction can take place by more than one route, and the initial and final concentrations are the same, the total enthalpy change is the same regardless of the route taken
Things to remember when using Hess’ law
If you have more than one compound, then you have to add the enthalpy of formation for each compound together
Enthalpy of formation is given for 1 mole of compound formed. If there is more than one mole, you multiply it
What is Hess’ law used for?
Hess’ Law determines enthalpy changes indirectly, for when determining them directly isn’t possible
Where does Hess’ law come from?
Hess’ Law comes from the idea of the conservation of energy
For elements, enthalpy change of formation is ALWAYS ____
zero
Enthalpy change of reaction equation =
sum of the enthalpy change of formation of products - sum of the enthalpy change of formation of reactants OR sum of the enthalpy change of combustion of reactants - sum of the enthalpy change of combustion of products
equation for rate of reaction
change in concentration (of products or reactants) / time
Units of rate of reaction
moldm^-3s^-1
Draw a graph of conc of reactants against time
check notes
Draw a graph of conc of products against time
check notes
What does the gradient of rates of reaction graphs show?
the rate of the reaction at that point
In collision theory, what must you remember?
Not all collisions are successful
High rate of reaction = what in terms of collision theory?
high number of successful collisions per second
A successful collision is
any collision that reaches the activation energy
Factors which alter rate of reaction:
- Temperature
- Surface area (solids)
- Catalysts
- Concentration
- Pressure (gases)
How does temperature affect ror?
At a higher temperature the particles have more kinetic energy, so more collisions are successful, and more frequent collisions, so higher rate of reaction
How does surface are affect ror?
At higher surface areas the particles have more places to collide into, so more successful collisions occur per second, so it’s a higher rate of reaction
How do catalysts affect ror?
Provide an alternative route for the reaction which lowers the activation energy, while remaining chemically unchanged. Lower activation energy, meaning more successful collisions per second, so faster rate of reaction
How does concentration affect ror?
Higher concentration, more particles per unit volume, so more successful collisions per second as more particles hitting into each other, so higher rate of reaction
How does pressure affect ror?
Higher pressure, more particles per unit volume, so more successful collisions per second as more particles hitting into each other, so higher rate of reaction
Describe general botzmann distribution curve
Every particle has energy No particles with no energy Most particles have medium energy A few particles have high energy Can’t touch x axis, must have an asymptote
Why must the boltzmann distribution curve have an asymptote?
cannot assume no particles with higher energy
Total area under boltzmann distribution curve is
the number of particles in the sample
Draw normal boltzmann distribution curve
Check notes
Show affect of catalyst on boltzmann distribution curve
Check notes
Show affect of temp (hot and cold) on boltzmann distribution curve
Check notes
Increase in concentration or pressure …
more particles in same volume more frequent collisions collisions over EA are more frequent rate of reaction increases
For a reaction to occur …
particles need to collide with sufficient energy and the correct orientation
Show affect of concentration on Boltzmann curve
check notes
A catalyst is
a substance that changes the rate of chemical reaction without undergoing a permanent change. It lowers the activation energy of the reaction by providing an alternative reaction pathway.
What is Effect of temperature on boltzmann curve
- As we increase the temperature the amount of energy increases so the curve moves to the right
- However we have no extra particles so the curve gets lower
- The area underneath the curve is the same as the number of particles hasn’t changed
- More particles now have sufficient energy to react
WHat is effect of concentration on boltzmann curve
- As we raise the concentration the amount of energy stays the same so the curve doesn’t move left or right
- However we have extra particles so the curve gets higher
- More particles now have sufficient energy to react
What is effect of catalyst on boltzmann curve
- If we introduce a catalyst an alternative reaction pathway with a lower activation energy is available
- More particles now have sufficient energy to react
Draw a diagram of how a catalyst works generally
Check notes
Draw potential energy diagram including catalyst
Check notes
Draw how catalyst works for ethene and hydrogen
check notes
Draw how catalyst works for hydrogen and carbon monoxide
check notes
Draw how catalysts work for ammonia in the haber process
check notes
How does a catalyst work?
- One of the reactants approaches the catalysts surface and settles onto an active site – adsorption
- Another reactant approaches the catalyst
- Re-arrangement of electrons takes place – reaction
- The products are released from the surface – desorption
Which metals are found in a catalytic converter?
Platinum, palladium and rhodium
What does a catalytic converter turn nitrogen oxide into?
Nitrogen and oxygen
What does a catalytic converter turn carbon monoxide molecules into?
Carbon dioxide
Heterogeneous catalysis is most frequently used in
industrial production processes
.Heterogeneous means that
the catalysts and starting molecules are present in different phases – for example, solid and gaseous – the gaseous starting particles react on the solid catalyst particles
Describe the process of heterogeneous catalysis
.The molecules approach the surface of the catalyst and stick to it in a defined arrangement
.The chemical bonds are cleaved with the aid of a catalyst
.The desired molecular bonds are formed, on completion of the reaction, the products leave the catalyst
A nickel catalyst can be used to
hydrogenate double bonds in an alkene
What does hydrogenating double bonds in an alkene do?
turn unsaturated fats, into saturated fats (vegetable oil into margarine)
A palladium catalyst can be used in a catalytic converter to combine what to produce what?
to combine 2 x CO molecules with a molecule of O2 to make 2 molecules of CO2
An iron catalyst is used in the _____ process
Haber
Why is a catalyst needed in the Haber process?
This ‘fixes’ nitrogen from the air using hydrogen and turns it into ammonia. This is very difficult to do without a catalyst as N2 has a triple bond and so has a high bond enthalpy (takes a lot of energy to break).
Explain why many industrial manufacturing processes use catalysts
Enables reactions to occur with less waste, enable reactions to happen with less toxic solvents/reactants, reactions can happen at room temperature, saves energy/cost, reduce carbon dioxide emissions, enable reactions to occur with more specify
Two methods can be used to determine the rate of reaction from gases, what are they?
- Monitoring the volume of gas produced at regular time intervals using gas collection
- Monitoring the loss of mass reactants using a balance at regular time intervals
When do you stop recording results when determining the rate of reaction?
You stop recording when the measured value does not change with time, this means the reaction is complete
How can catalysts work?
The catalyst may react with a reactant to form an intermediate or may provide a surface on which the reaction can take place
At the end of the reaction the catalyst is regenerated
What is a homogenous catalyst and how does it work?
A homogenous catalyst has the same physical state as the reactants. The catalyst reacts with the reactants to form an intermediate, the intermediate then breaks down to give the product and regenerates the catalyst.
Give an example of a homogenous catalyst
An example would be making esters with sulfuric acid as the catalyst, all ethanol, ethanoic acid and sulfuric acid are liquids.
What does the honeycomb mesh in catalytic converters do?
.Honeycomb mesh provides a large surface area for the reaction to take place
The economic costs of using a catalyst outweigh …
any costs associated with developing a catalytic process
How do you know when it is a reversible reaction?
The double arrows
What is a reversible reaction?
When the reaction can go forwards and backwards
What are reversible reactions described as?
dynamic, they are continuous
There comes a point where the rate of the rate of the forward reaction equals the rate of the backwards reaction, this is called …
Dynamic equilibrium
The concentrations of all the particles in the system remain constant, this is because …
the rate of reaction in one direction is equal to the rate of reaction in the other direction
Dynamic equilibrium’s must remain in a closed system, why?
matter cannot enter or exit, as if it did it would ruin the equilibrium
What conditions change the position of equilbrium?
.Concentration of the substances
.Temperature of system
.Pressure of system for gasses
.Presence of a catalyst
What is le chatelier’s principle?
‘When a system in dynamic equilibrium, is subjected to a change, the position of the equilibrium will shift to minimise the change’
Shifting the reaction to the left means to …
Increase the concentration of the reactants
Shifting the reaction to the right means to …
Increase the concentration of the products
If you increase the concentration of one of the products, the reaction …
shifts to the left and increases the amount of reactants being formed, thereby increasing their concentration and keeping the concentration of all particles in the system constant
If you increase the concentration of one of the reactants, the reaction …
shifts to the right and increases the amount of products being formed, thereby increasing their concentration and keeping the concentration of all particles in the system constant
If you decrease the concentration of one of the products, the reaction …
shifts to the right and increases the amount of products being formed, thereby increasing their concentration and keeping the concentration of all particles in the system constant
If you decrease the concentration of one of the reactants, the reaction …
shifts to the left and increases the amount of reactants being formed, thereby increasing their concentration and keeping the concentration of all particles in the system constant
Changing the pressure only works for which state?
Gasses
For working out the favoured reaction with pressure changes and le chateliers principle, what must you do first? What equation do you do this with?
First you must establish which side of the reaction has the greater volume
moles = volume / 24
An increase in pressure responds by shifting the reaction to …
The side with the fewest moles
A decrease in pressure responds by shifting the reaction to
The side with the most moles
Regarding le chateliers principle, if moles/volume equal on both sides, a change in pressure would
not cause an increase in one reactions rate of reaction, both would have an increase in rate of reaction
What does a catalyst do for le chateliers reaction?
The catalyst increases the rate of the forward and backwards reaction by the same amount, so the position of equilibrium not effected
When using temperature for le chateliers reaction, what must we do first?
We need to know which reaction is exothermic and which reaction is endothermic
For le chateliers principle, an increase in temperature causes …
an increase in the rate of the endothermic reaction, the endothermic reaction is favoured
For le chateliers principle, a decrease in temperature causes …
an increase in the rate of the exothermic reaction, the exothermic reaction is favoured
Describe how a dynamic equilibrium comes about?
.At the start of the reaction, the concentrations of A and B were at their maximum
.This means that the rate of reaction was at its fastest
.As A and B react, their concentrations fall
.That means that they are less likely to collide and react, and so the rate of the forward reaction falls as time goes on
.In the beginning there isn’t any C and D so there can’t be any reaction between them
.As time goes on, though, their concentrations in the mixture increase and they are more likely to collide and react
.With time, the rate of reaction between C and D increases
.Eventually the rates of the two reactions will become equal
.A and B will be converting into C and D at exactly the same rate as C and D convert back into A and B again
.At this point there won’t be any further change in the amounts of A, B, C and D in the mixture
.As fast as something is being removed, it is being replaced again by the reverse reaction
.We have reached a position of dynamic equilibrium
Dynamic equilibrium is reached when …
the rate of the forward reaction is the same as the backwards reaction, concentrations of reactants and products remain constant
The Haber process takes place at 350’c-500’c and 100-200 atm, why?
these conditions produce the most ammonia in the dynamic equilibrium, but are also the most cost efficient
Haber Process, pressure conditions, ideal, problem and actual
Ideal - high
problem - high danger
actual - 200ATM
Haber Process, temperature conditions, ideal, problem and actual
Ideal - low
problem - rate low
actual - 400-500’C
What catalyst is used in the Haber process?
Fe
What are the actual conditions of the haber process called? Why?
These actual conditions are called compromise conditions, as they are compromising on the yield but they will be able to gain this product in shorter time frame
What is the yield of the haber process?
15%
What happens to unsused nitrogen and hydrogen in the haber process?
it is recycled through the process again
Kc =
[products] / [reactants]
[ ] =
equilibrium concentrations in moldm-3
If the equation was aA + bB cC + dD, what would Kc equal?
([C]c x [D]d) / ([A]a x [B]b)
What is Kc?
The equilibrium, constant but it is temperature dependant
An increase in temperature does what to Kc in the case of a forward exothermic reaction?
An increase in the temperature increases the concentration of reactants and lessens that of the products so Kc decreases
A decrease in temperature does what to Kc in the case of a forward exothermic reaction?
A decrease in the temperature decreases the concentration of the reactants and increases that of the products so Kc increases
What does a large Kc mean?
equilibrium is favouring the right hand side
What does a small Kc mean?
equilibrium is favouring the left hand side
The magnitude of Kc indicates what?
the relative proportions of reactants and products in the equilibrium system
A rough guide as to what the magnitude of Kc indicates
- A Kc value of 1 indicates a position of equilibrium that is halfway between reactants and products
- A Kc value > 1 indicates a position of equilibrium that is towards the products
- A Kc value < 1 indicates a position of equilibrium that is towards the reactants
So the larger the Kc value, the further the …
… position of equilibrium lies to the right-hand side and the greater the concentrations of the products compared to the reactants
