Physical Flashcards
What are the different sub shells and how many orbitals and electrons do they have?
s 1 2
p 3 6
d 5 10
f 7 14
What are the exceptions to electron configurations?
Chromium 4s1 3d5
Copper 4s1 3d10
How do you find the electron configuration of ions?
Write out the normal one and then take away from the highest no. orbital (or add if anion)
What is ionisation energy?
The energy required to remove 1e- from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous ions
What factors affect ionisation energies?
Charge of the nucleus
Atomic radius
Shielding
How does the charge of the nucleus affect IE?
Increased charge means increased IE as stronger attraction between electron and nucleus
How does distance from nucleus affect IE?
Increased distance means decreased IE as weaker attraction between electron and nucleus
How does shielding affect IE?
Increased shielding means decreased IE as weaker attraction between electron and nucleus
What is the trend in Ionisation Energy down groups?
Decreases as there is increased shielding and distance from nucleus
What is the trend in Ionisation Energy across periods?
Increase due to increased nuclear charge and decreased distance (similar shielding)
What are the four stages of mass spectrometry?
Ionisation
Acceleration
Ion Drift
Detection
How does the ionisation stage of mass spectrometry work?
Electron gun - fires high energy electrons which knock off an electron to create a cation
Electrospray Ionisation - sample is dissolved and pushed through a small nozzle at high pressure. A high voltage is applied to it so each atom gains a H+
How does the acceleration stage of mass spectrometry work?
All ions given same KE as accelerated through electric field
How does ion drift stage of mass spectrometry work?
Allows ions of different mass to separate (all have same KE so will have different velocities)
How does the detection stage of mass spectrometry work?
Detector creates a current by grabbing an electron from the ion when it hits it, the greater the current the greater the abundance
Why do successive ionisation energies of the same atom increase?
Electron are being removed from an increasingly positive ion
There’s less repulsion amongst the remaining electrons so there’s a greater attraction to the nucleus
Ideal gas equation?
pV=nRT
What is the empirical formula?
The simplest whole number ratio of atoms of each element in a compound
How do you find atom economy?
Mr of desire product / sum of Mr of all reactants x 100
What are the properties of ionic bonding?
High mp and bp as lots of energy required to overcome the strong electrostatic force of attraction
Conduct electricity when molten or aqueous as ions are free to move
Dissolve in water as water molecules are polar causing the ions to pulled away from the lattice causing it to dissolve
What are the properties of macromolecular structures and give some examples?
diamond and graphite
High mp and bp as strong electrostatic force of attraction
Good thermal conductor as vibrations travel easily through the stiff lattice
What is graphite and what is it properties?
Carbon atoms arranged in sheets of hexagons where each carbon is bonded to three others
Slippery (can be used as a dry lubricant) as weak VDW between layers so can easily slide over each other
Electrical conductor as free electron for very carbon atom
Low density as layers are far apart
Insoluble in any solvent as covalent bonds too strong
What are the properties of molecular structures?
Low mp and bp as only wear inter molecular forces between molecules
Doesn’t conduct electricity
Can be soluble but depends on how polarised the molecule is
What is dative covalent bonding?
Where both electrons in the shared pair come from the same atom
What are the properties of metallic bonding?
High mp and bp due to strong electrostatic force of attraction
Good thermal conductor as delocalised electrons can easily transfer kinetic energy
Insoluble due to strength of bonds (except in liquid metals)
What affects the melting point of metals?
no. of delocalised electrons per atom as the more there are the stronger the bonding will be
size of metal ions as smaller ions will have smaller distance between nucleus and electrons so stronger bonds
Why are solids incompressible?
Particles are very close together so have a high density
Why are ionic substances often brittle?
When layers of alternating change are distorted, the like charges then line up and repel breaking the lattice into fragments
Why are metals quite hard (not brittle)?
Delocalised electrons prevent fragmentation
Name and bond angle when co-ord. no is 2?
linear 180
Name and bond angle when co-ord. no is 3?
trigonal planar 120
Name and bond angle when co-ord. no is 4?
tetrahedral 109.5
Name and bond angle when co-ord. no is 5?
trigonal bipyramidal 90 and 120
Name and bond angle when co-ord. no is 6?
octahedral 90
Name and bond angle when 2 bonding pairs and 2 lone pairs?
bent 104.5
Name and bond angle when 3 bonding pairs and 1 lone pair?
trigonal pyramidal 107
What is electronegativity?
The power of an atom to attract the pair of electrons in a covalent bond
What is the electronegativity trend down groups?
Decreases because shielding increases
What is the electronegativity trend across periods?
Increases as atomic radius decreases
When do you get polar bonds and what do they do?
When the two atoms that are bonded have very different electronegativties, the more electronegative one will draw the electrons towards itself creating delta charges and creating a permanent dipole-dipole
When is a molecule polar?
When a molecule had polar bonds and there is an uneven distribution of charge across the whole molecule
When a molecule has polar bonds that are symmetrical the changes cancel out do no permeant dipole
What properties do intermolecular forces affect?
Physical properties eg mp
What are Van Der Waals forces and how do they form?
Weak IMF that cause all molecules to be attracted to each other
Electrons in charge clouds are always moving causing the charge density at any one time to be uneven creating temporary dipoles
One temporary dipole will then induce another temporary dipole in a neighbouring atom/molecule which then creates a domino effect
Dipoles are constantly being created and destroyed but the overall effect is atoms are attracted to each other
What makes Van Der Waals stronger?
Larger Mr as larger molecules have larger electron clouds
What has stronger VDW branched or straight chain molecules?
Straight chain as can lie closer together which reduces the distance over which the forces act making them stronger
With what atoms does hydrogen bonding occur?
Fluorine, Oxygen and Nitrogen
Why do hydrogen bonds arise?
F, O and N are very electronegative so they draw electrons away from from the hydrogen atom. The bond is so polarised and hydrogen has such a high charge density (as its so small) that its able to form hydrogen bonds with the lone pairs of electrons on the F,O and N of other molecules
What must you include on a hyrdogen bond diagram?
Partial charges
Lone pair of electrons
Labelled hydrogen bond
Why does ice float?
Ice is less dense than water
When water cools to make ice, the molecules form more hydrogen bonds and arrange themselves in a regular lattice structure. In this lattice the H2O molecules are further apart causing it to expand and make it less dense
What is enthalpy change of formation?
Enthalpy change when one mole of a substance is formed from its constituent elements under standard conditions
What is enthalpy change?
The heat energy transferred in a reaction at constant pressure
What is an exothermic reaction?
When energy is given out (ΔH negative)
What is an endothermic reaction?
Energy is taken in from the surroundings (ΔH positive)
What is mean bond enthalpy?
The average energy needed to break a certain type of bond over a range of compounds
What is calorimetry?
An experimental method for finding enthalpy change by measuring temperature change over time
What is specific heat capacity?
The amount of energy required to increase the temperature of 1kg of a substance by 1oC
Why can calorimetry be inaccurate?
Energy easily lost through conduction and convection
Incomplete combustion
Flammable liquids are often volatile so may loose fuel to evaporation
Experiment not carried out in standard conditions
What is Hess’s Law?
The total enthalpy change of a reaction is independent of the route taken
What is reaction rate?
The change in amount of reactant or product produced per unit time
What affect does increasing conc. or pressure of reaction have?
Rate increases as on average molecules are closer together (as more molecules per unit volume) so frequency of collisions increases so the no. successful collisions also increases
What is a catalyst?
A substance that increases the rate of reaction without being used up in the reaction
How does a catalyst work?
Provides an alternative reaction route with a lower activation energy
Affect of catalyst on Maxwell Boltzmann Distribution?
Shifts Ea left
Affect of increased conc. or pressure on Maxwell Boltzmann Distribution?
Curve shifts right
What affect does increasing temp. have on rate of reaction?
Thermal energy is transferred to kinetic. The molecules move faster and have more energy meaning the frequency of collisions increases and more have energy greater than the activation energy so rate increases.
Affect of increases temp. on Maxwell Boltzmann Distribution?
Shifts right
What must a successful collision have?
Energy greater than the activation energy
Molecules must collide in the right direction
What is the activation energy?
Minimum amount of kinetic energy that particles need to react
What goes on the x-axis and y-axis of Maxwell Boltzmann distribution?
x-axis Kinetic energy
y-axis. No. molecules
What does the area under the Maxwell Boltzmann Distribution represent?
Total no. molecules
What does the peak of the Maxwell Boltzmann Distribution represent?
Most probable energy
What is dynamic equilibrium?
When the forward and backwards reaction occur at the same rate, conc of reactants and products are constant. Must be a closed system.
What is Le Chatelier’s principle?
If a reaction at equilibrium is subjected to a change in concentration, pressure or temperature, the position of equilibrium will move to counteract the change
What are the conditions for equilibria?
Rate of forward and backward reaction are the same
Conc. of reactants and products are not changing
What is a homogeneous equilibria?
When every species is in the same physical state
When can Le Chatellier be applied?
Homogenous equilibria
What happens to the equilibrium when conc. of a species is increased?
Shifts in the opposite direction of species to get rid of the extra species
What happened to the equilibrium when conc. of a species is decreased?
Shifts in direction towards species to make more of that species
When does pressure affect equilibria?
When in gaseous states
How does increasing pressure affect the position of equilibrium?
Shifts to side with fewer moles to reduce pressure
How does decreasing pressure affect the position of equilibrium?
Shifts to side with more moles to increase pressure
How does increasing temp affect the position of equilibrium?
Favours endothermic direction so that it can absorb the heat
How does decreasing temp affect the position of equilibrium?
Favours exothermic direction to produce more heat
How do catalyst affect the position of equilibrium?
No effect
Can’t increase yield but allow equilibrium to be reached faster
What is the Haber Process?
Ammonia production
N2 (g) + 3H2 (g) –>2NH3 (g)
What conditions are used in the Haber Process?
200 atm
450 °c
iron catalyst
What catalyst is used in the Haber Process?
Iron
What must remain constant for Kc to be constant?
Temperature
What factors affect Kc and which ones don’t?
Temp. does
Conc. and catalyst doesn’t
What is oxidation?
Loss of electrons
What is reduction?
Gain of electrons
What is a redox reaction?
When oxidation and reduction happen simultaneously
What is an oxidising agent?
Accepts electrons and gets reduced
What is a reducing agent?
Donates electrons and gets oxidised
What does the oxidation state of an element tell you?
The total number of electrons it has donated or accepted
Oxidation state of group 7 and exception?
-1 except when bonded with Fluorine
Oxidation state of hydrogen and exception?
+1 except in metal hydrides
Oxidation state of oxygen and exception?
-2 except H2O2
What is lattice dissociation enthalpy?
The enthalpy change when 1 mole of a solid ionic compound is completely dissociated into its gaseous ions under standard conditions
What is lattice formation enthalpy?
The enthalpy change when 1 mole of a solid ionic
compound is formed from its constituent gaseous ions under standard conditions
What is atomisation enthalpy?
The enthalpy change when one mole of gaseous atoms is formed from its constituent element under standard conditions
What is the enthalpy of electron affinity?
The enthalpy change when one mole of electrons is added to a mole of gaseous atoms under standard conditions
What is enthalpy of solution?
The enthalpy change when one mole of an ionic solid dissolves in an infinite amount of water so that the dissolved ions are separated and do not interact with each other, under standard conditions
What is the enthalpy of hydration?
The enthalpy change when one mole of gaseous ions is dissolved in an infinite amount of water to form to one mole of aqueous ions under standard conditions
What does the perfect ionic model assume?
All ions are perfectly spherical
Ions display no covalent character
Charge is evenly distributed
What influences hydration enthalpy?
Size and charge of the molecules
When does covalent character occur?
When the two ions have varying sizes and charges meaning the distribution of charge is uneven
What does a large difference between theoretical and experimental values mean for enthalpy of solution?
Strongly polarised bonds meaning lots of covalent character
What is normally bigger theoretical or experimental value for enthalpy of solution?
Experimental due to the presence of covalent character making the bonds stronger
What is entropy?
Measure of disorder
What does feasible mean in terms of a reaction?
Reaction will occur spontaneously
When are substances more energetically stable?
When they have a higher entropy (more disorder)
What is free energy change ΔG?
A measure used to predict wether a reaction is feasible
When is a reaction feasible?
ΔG ≤ 0 (negative)
What is the equation for free energy change ΔG?
ΔG = ΔH - TΔS
What is the equation for entropy?
ΣS products - ΣS reactants
How do you find the order of a reaction?
Through experiments, it can’t be found from chemical equations
How does temp. affect k in rate equations?
When temp. increases, k increases
What does the A stand for in Ahrrenius equation and what are the units?
Arrhenius constant s -1
What is the rate determining step?
The slowest step in a reaction
How do you find the rate of reaction from a conc. - time graph?
Draw a tangent at t=0 and calculate the gradient
Why do you draw the tangent at t=0 when determine the rate from a conc. - time graph?
This is the only time when the exact conc. of reactants is known
How do you find the order of a reaction from conc. - time graphs?
Repeat using different concentrations.
Plot a graph of the calculated rates against initial conc. of reactants
The shape of the graph will tell you the order
Define the term overall order of reaction
The sum of powers to which the concentrations are raised in the rate equation
When can Kp be calculated?
When all reactants and products are in their gaseous state in an equilibrium
How do you calculate partial pressure?
Partial pressure p(A) = mole fraction of A x total pressure P
What are the units of partial pressure?
Pascal or atmosphere
What does the sum of all the partial pressures equal?
Total pressure
Does changing pressure affect Kp, why?
No because eqm. shifts to keep Kp the same
Does catalyst affect Kp?
no
What affects Kp?
temp
What type of reaction do electrochemical cells use?
redox
What does the salt bridge do and what is made of?
Filter paper soaked in unreactive ions (e.g KNO3) and it completes the circuit by allowing electrons to flow but won’t interfere with the reaction
In cell representation what goes on the left?
More negative potential, oxidation
What goes in the middle next to the salt bridge in cell representation?
The most oxidised species (most positively charged species)
When do you include a phase boundary in cell representation?
When its in a different state
What are the standard conditions electrochemical cells?
all solutions 1moldm-3 conc.
298K
100kPa
What is the standard electrode potential?
The voltage measured under standard conditions when a half cell is connected to a standard hydrogen electrode.
When is a platinum electrode used?
If there is no metal involved in the half cell reaction
Why is a platinum electrode used?
Inert and conducts electricity
Which is the LHS in an electrochemical cell?
More negative EMF
Which side of the electrochemical cell is oxidation occurring?
LHS
Which side of the electrochemical cell is reduction occurring?
RHS
What does a negative EMF mean?
Substances are more easily oxidised so will lose electrons
What does a positive EMF mean?
Substances are more easily reduced so will gain electrons
How do you calculate the EMF of a cell?
E cell = Erhs - Elhs
E cell = Ered - Eox
more positive value - more negative value
What does a positive cell potential value mean?
Reaction taking place is spontaneous and favourable
Which is the best oxidising agent in an electrochemical series?
bottom left (most positive emf value)
Which is the best reducing agent in an electrochemical series?
top right (most negative emf value)
What affect does increasing the conc. of solutions used in electrochemical cells have on the cell EMF?
Makes the cell EMF more positive as fewer electrons are produced in the reaction
What affect does increasing the pressure of the cell have on the cell EMF?
Makes the cell EMF more negative as more electrons are produced
What is a use of electrochemical cells?
Useful source of energy for commercial use
When is a cell rechargeable?
When the cell is a reversible reaction meaning the reactants can reform
What is an example of a rechargeable battery and where is it used?
Lithium ion cells and used as rechargeable batteries in phones, laptops and cars
What are the two electrodes in a lithium ion cell?
Lithium cobalt oxide electrode and a graphite electrode
What occurs at the negative electrode?
oxidation
What occurs at the positive electrode?
Reduction
Equation for negative electrode of lithium ion cell?
Li –> Li+ + e-
Equation for positive electrode of lithium ion cell?
Li+ + e- + coO2 –> Li+[CoO2]-
How do you recharge a cell?
Supply a current over the cell which forces electrons to move in the opposite direction, causing the reaction to reverse
Why are some cells non-rechargeable?
The reactions used are impossible to reverse
Where are fuel cells used?
Used to generate an electrical current
What is an example of a fuel cell and how does it work?
Hydrogen Fuel Cell
Uses a continuous supply of hydrogen and oxygen from air to generate a continuous current
Why is the hydrogen fuel cell seen as environmentally friendly?
Only waste product is water
What are the disadvantages of a Hydrogen Fuel Cell?
Hydrogen is highly flammable
Very expensive to produce
Need energy to produce supply of hydrogen and oxygen which comes from fossil fuels
What are the advantages of fuel cells?
More efficient than internal combustion engine
Only waste product is water
Don’t need to be recharged
In a fuel cell how are chemicals stored?
Stored separately outside the cell and are fed in when electricity is required
What is the equation at the negative electrode of an alkaline hydrogen fuel cell?
H2(g) + 2OH- (aq) —> 2H2O + 2e-
What is the equation at the positive electrode of an alkaline hydrogen fuel cell?
O2 (g) + 2H2O (l) + 4e- —> 4OH- (aq)
What is the overall reaction of a Hydrogen fuel cell?
H2 (g) + 0.5 O2 (g) –> H2O (g)
What is the meaning of the term electrochemical series?
List of half cells in order of electrode potentials
How do you maintain emf of cell when in use?
keep concentration of reactants constant (or constantly add reactants)
What is a Bronsted Lowry acid?
proton donor
What is a Bronsted Lowry base?
proton acceptor
What is pH?
measure of hydrogen ion concentration
How do you calculate pH?
pH = -log[H+]
How do you calculate [H+]?
[H+] = 10^-pH
Why is pH a logarithmic scale?
Because the concentration of H+ ions in a solution can vary enormously
What is a strong acid?
An acid that completely dissociates in solution
What is a strong base?
A base that completely dissociates in solution
What is a weak acid?
An acid that only partially dissociates in solution
What is a weak base?
A base that only partly dissociates in solution
What is the equation for Kw?
Kw = [H+][OH-]
How do you get Kw from Kc?
Because water only dissociates a tiny amount we can assume the conc. of water is constant as it so much larger than [H+] and [OH-]. So Kc[H2O] = [H+][OH-] but we can treat the LHS as one constant Kw
When does the neutral point of water change and why?
When temp. changes pH decreases as reaction is endothermic so eqm shifts right and [H+] increases and Kw = [H+]^2
When do we use Kw?
Calculations with strong acids and strong bases
When do we use Ka and why?
Weak acids because strong acids dissociate almost completely so we can’t make the same assumptions
What is the equation for Ka?
Ka = [H+][A-]/[HA]
What two assumptions do we make when using Ka?
As it is a weak acid, only tiny amount dissociates so [HA] at equilibrium is the same as [HA] at the start
Assume the dissociation of acid is much greater than the dissociation of water so assume all H+ ions come from acid.
Then we can say [H+] = [A-]
Ka = [H+]^2 / [HA]
What is a buffer?
A solution that resists change in pH when small volumes of acid or base are added
What is an acidic buffer made of?
weak acid and its salt
When you add acid to an acidic buffer how does it resist changes to pH?
When you add H+ it reacts with the salt which has completely dissociated to make more acid meaning [H+] remains constant
When you add a base to an acidic buffer how does it resist changes to pH?
The OH- ions react with H+, the eqm. of the weak acid then shifts right to replace the H+ ions lost so [H+] remains constant
Why must a buffer solution be weak acid?
Strong acid has completely dissociated.
So when you add acid, once the H+ has reacted with the salt to make the acid it will just dissociate
When you add a base, the eqm. cant shift right as is already very far over to the right do its unable to replace H+ ions that were lost
What is a basic buffer made of?
weak base and its salt
What happens when you add acid to a basic buffer?
H+ reacts with OH- so eqm. shifts right to replace OH- lost
What happens when you add a base to a basic buffer?
It reacts with the positive ion from the dissociation of the salt
What are some uses of buffers?
Shampoos - require a pH buffer of 5.5 as hair becomes rough when exposed to alkaline conditions
Biological buffer systems - enzymes only work at certain pHs so lots in our body eg blood needs a pH of 7.4
What is a diprotic acid?
an acid that can donate two protons per molecule
What is the vertical point of a pH curve?
Equivalence point
What happens at the equivalence point when you’re carrying out a titration?
A tiny amount of base or acid will result in a sudden big change in pH
What colour is methyl orange in acid?
red
What colour is methyl orange in a base?
yellow
What is the pH range where methyl orange will change colour?
3-5
What colour is litmus in acid?
red
What colour is litmus in a base?
blue
What pH range does litmus change colour?
5-8
What colour is phenolphthalein in acid?
colourless
What colour is phenolphthalein in basic conditions?
pink
What pH range does phenolphthalein change colour?
8-10
How do you decide what indicator to use?
The pH range of the colour change of the indicator must lie entirely in the vertical part of the pH curve
What indicator should you use for strong acid, strong base?
any
What indicator should you use for strong acid, weak base?
methyl orange
What indicator should you use for weak acid, strong base?
phenolphthalein
When does pH = pKa?
half equivalence point
When making a buffer solution by mixing a monoprotic acid (e.g. HA) and a base (e.g NaOH) must be in excess and why?
Acid must be in excess
Acid + base makes salt which will give you A- ions but then you also need there to still be acid, HA, left as a buffer solution is made of a weak acid and its salt
What is a conjugate base?
substance formed when acid has lost proton
What is the cell representation of an alkaline hydrogen fuel cell?
Pt | H2 (g) | OH- (aq) , H2O (l) || O2 (g) | H2O (l) , OH- (aq) | Pt
What are the units for entropy?
J K-1 mol-1
Why is an aqueous electrolyte not used in lithium cells?
Lithium would react with the water
