A2 Chemistry Equilibria, Energetics and Elements (OCR F325)

A comprehensive revision guide made using the OCR syllabus so that everything is covered. Quite detailed so not ideal if your after quick notes, but theyre more condensed than a text book. Some extra detial to help answer the "suggest why" questions we all know and hate. Hope these can come in useful :)

Preview of A2 Chemistry Equilibria, Energetics and Elements (OCR F325)

Extracted text:

Chemistry F325
Contents
Rates, Equilibrium and pH ................................................................................................................. 1
How Fast?...................................................................................................................................... 1
Rate equations........................................................................................................................... 1
Determining orders.................................................................................................................... 2
The rate constant....................................................................................................................... 3
Rate determining step ............................................................................................................... 4
How Far? ....................................................................................................................................... 4
Determining equilibrium concentrations .................................................................................... 5
The equilibrium constant ........................................................................................................... 5
Acids, Bases and Buffers ................................................................................................................ 6
Acid reactions ............................................................................................................................ 6
Conjugate acid base pairs .......................................................................................................... 7
Acid dissociation constant.......................................................................................................... 8
Ionic product of water ............................................................................................................... 8
pH ............................................................................................................................................. 8
Buffers ..................................................................................................................................... 10
Neutralisation .......................................................................................................................... 11
Energy ............................................................................................................................................. 14
Born-Haber cycles........................................................................................................................ 14
Lattice enthalpy ....................................................................................................................... 14
Enthalpy of formation .............................................................................................................. 15
Enthalpy of atomisation ........................................................................................................... 15
Ionisation energy ..................................................................................................................... 15
Electron affinity ....................................................................................................................... 15
Constructing Born-Haber cycles ............................................................................................... 16
Enthalpies of solution and hydration ........................................................................................ 17
Entropy ....................................................................................................................................... 17
Free energy ............................................................................................................................. 18
Electrode Potentials and Fuel Cells .............................................................................................. 18
Redox ...................................................................................................................................... 19

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Page 2

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Chemistry F325 31/12/2012 10:38
Electrode potentials................................................................................................................. 19
Feasibility of reactions ............................................................................................................. 22
Storage cells ............................................................................................................................ 23
Fuel cells.................................................................................................................................. 23
FCVs ........................................................................................................................................ 24
Hydrogen economy.................................................................................................................. 25
Transition elements ......................................................................................................................... 26
Properties.................................................................................................................................... 26
Electron configurations ............................................................................................................ 26
Physical properties .................................................................................................................. 26
Precipitation reactions ................................................................................................................. 27
Ligands and Complex Ions............................................................................................................ 27
Monodentate ligands............................................................................................................... 27
Bidentate ligands ..................................................................................................................... 28
Stereoisomerism...................................................................................................................... 28
Ligand substitution ...................................................................................................................... 30
Haemoglobin ........................................................................................................................... 30
Stability constants ................................................................................................................... 31
Redox reactions and Titrations .................................................................................................... 31
Manganate titrations ............................................................................................................... 32
Thiosulphate titrations.............................................................................................................

Page 3

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Chemistry F325 31/12/2012 10:38
Rates, Equilibrium and pH
How Fast?
Rate of reaction is the change in concentration of a reactant or product per unit time
The units of rate are mol dm-3 s-1
Rate of reaction can be determined from a concentration time graph
This can be concentration of reactant or product
The initial rate can be calculated by finding the gradient of concentration time graph at t=0
This gives the rate of decrease in concentration
of reactants.

Page 4

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Chemistry F325 31/12/2012 10:38
If the order with respect to a reactant A is 1, then rate is proportional to [A], so if [A] doubles,
rate also doubles
If the order with respect to a reactant B is 2, then rate is proportional to [B]2 so if [B] doubles,
rate quadruples
The orders of reaction can ONLY be determined from experimental data and not the equation
The units of the rate constant, k, can be determined using the formula
o Units of k = (mol

Page 5

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Chemistry F325 31/12/2012 10:38
Half lives
Half-life of a reactant is the time taken for the concentration of the reactant to reduce by half
All first order reactants have a constant half-life (it is independent of concentration)
Zero order reactions have a decreasing half-life with time
Second order reactions have an increasing half-life with time
Concentration of reactant
This is the half-life of a first
order reaction as concentration
has halved from the initial
Time
Initial rates
Clock reactions are where the time taken from

Page 6

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Chemistry F325 31/12/2012 10:38
Use the specific values of rate and concentration for one experiment
If the data is reliable, all experiments should have data which calculates the same or a very
similar value of k
Effect of temperature
Increasing temperature means molecules have more energy, which has two effects:
o Increasing the number of collisions
o Increasing the number of molecules that possess sufficient energy to overcome the
activation energy barrier
These compound to allow rate to increase rapidly with temperature
Rate doubles for

Page 7

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Chemistry F325 31/12/2012 10:38
o The rate of the forward and reverse reactions are the same
o The concentrations of reactants and products stay constant
However, this does not mean that the concentration of reactants equals the concentration of
products (they just remain constant at equilibrium)
The position of equilibrium is used to describe the relative proportions of reactants and products
A POE (position of equilibrium) over to the RHS (right hand side) has a higher concentration of
products
A POE over to the LHS

Page 8

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Chemistry F325 31/12/2012 10:38
When kc < 1, the POE is over to the LHS
Temperature is the ONLY thing that affects the value of kc
Effect of temperature
Forward reaction is endothermic
An increase in temperature will favour the forward direction to oppose the change (by Le
Chatelier's principle)
More products will be produced, so kc increases
Forward reaction is exothermic
An increase in temperature will favour the reverse direction to oppose the change (by Le
Chatelier's principle)
More reactants will be produced, so

Page 9

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Chemistry F325 31/12/2012 10:38
Acid reactions can be written in terms of the H+ ions and the ions they react with
This is called an ionic equation
The other ions not involved in the reaction are called spectator ions and are excluded from the
ionic equation
Acids participate in reactions readily with:
o Carbonates
o Bases
o Alkalis
o Metals
Even if a weak acid only partly dissociates H+ ions, as the reaction progresses, the H+ ions become
used up
o The equilibrium reaction releasing

Page 10

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Chemistry F325 31/12/2012 10:38
However, in each acid base equilibrium, there are two acid-base pairs
o The other in this case is the base H2O accepting a proton to form its conjugate acid, H3O+
Acid dissociation constant
There are comparatively few strong acids (acids which fully dissociate in solution
o HCl
o HNO3
o H2SO4
o HBr
o HI
o HClO4
Weak acids are more common:
The general, weak, monobasic acid has the following dissociation equilibrium reaction:
o HA(aq) + H2O(l) H3O+(aq) + A-(aq)
o

Comments

Zaynab

Sun 18th August, 2013 @ 20:40

Thank you sooo much for these AMAZING notes. Can you please kindly post F324 notes aswell (if you have them).

pali'

Mon 2nd December, 2013 @ 19:37

Thank you for the notes; they were really helpful. Do you have any for F324? Please could you put then up please! Your a life saviour.

Alex`

Sun 19th October, 2014 @ 15:05

do you guys have these notes ^

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