TOPIC 01 • KINETICS
How Fast? — Rates of Reaction
Reaction kinetics describes how quickly chemical reactions occur and how the rate changes when conditions are altered.
Rate of Reaction
Rate can be measured using the change in concentration of a reactant or product per unit time.
Initial Rate
The initial rate is the rate of reaction at the beginning of a reaction. It can be determined from the gradient of a tangent to a concentration-time graph at t = 0.
Factors Affecting Rate
- Concentration of reactants
- Pressure of gaseous reactants
- Temperature
- Surface area
- Presence of a catalyst
Collision Theory
Particles must collide with sufficient energy and suitable orientation for a successful reaction.
The minimum energy required for particles to react successfully during a collision.
TOPIC 02 • RATE EQUATIONS
Rate Equations
Experimental data can be used to determine how the concentrations of reactants affect reaction rate.
Orders of Reaction
- Zero order: rate is independent of concentration.
- First order: rate is proportional to concentration.
- Second order: rate is proportional to concentration squared.
Overall Order
The rate constant, k, depends on temperature and its units depend on the overall order of the reaction.
Compare experiments where only one concentration changes. This allows the order with respect to that reactant to be determined.
TOPIC 03 • ARRHENIUS
Temperature and the Arrhenius Equation
Increasing temperature generally increases reaction rate because a greater proportion of particles have energy greater than the activation energy.
Arrhenius Equation
- k = rate constant
- A = pre-exponential factor
- Eₐ = activation energy
- R = gas constant
- T = temperature in kelvin
Arrhenius Plot
For a graph of ln k against 1/T, the gradient is −Eₐ/R.
TOPIC 04 • THERMODYNAMICS
How Far? — Entropy
Entropy is a measure of the disorder or dispersal of energy and particles in a system.
Entropy and Physical State
- Gases generally have higher entropy than liquids.
- Liquids generally have higher entropy than solids.
- Increasing the number of gas particles generally increases entropy.
Total Entropy Change
A process is thermodynamically feasible when ΔStotal is positive.
TOPIC 05 • EQUILIBRIUM
Equilibria
Dynamic equilibrium occurs when the forward and reverse reactions continue at equal rates in a closed system.
Equilibrium Constant
Le Chatelier's Principle
When a system at equilibrium is subjected to a change, the equilibrium position shifts in the direction that opposes the change.
Industrial Equilibria
Industrial processes must balance equilibrium yield, reaction rate, economic cost, energy requirements and safety.
TOPIC 06 • ACID–BASE
Acid–Base Equilibria
Acids and bases can be treated as equilibrium systems, particularly when considering weak acids and weak bases.
Weak Acid Equilibrium
Acid Dissociation Constant
pH
Buffer Solutions
Buffer solutions resist changes in pH when small amounts of acid or alkali are added.
Titration Curves
Titration curves show how pH changes as acid or alkali is added and can help identify the equivalence point and suitable indicator.
A buffer contains a weak acid/base and its conjugate partner, allowing added H+ or OH− to be removed by equilibrium reactions.
TOPIC 07 • ORGANIC CHEMISTRY
Carbonyl Compounds
Aldehydes and ketones contain the carbonyl functional group, C=O.
Aldehydes
Aldehydes contain the functional group −CHO and can be oxidised to carboxylic acids.
Ketones
Ketones contain a carbonyl group bonded to two carbon groups and are generally resistant to further oxidation.
Nucleophilic Addition
Nucleophiles can attack the electrophilic carbon atom of the carbonyl group.
Reaction with Hydrogen Cyanide
Aldehydes and ketones can react with hydrogen cyanide to form hydroxynitriles.
The carbonyl carbon is electron deficient because oxygen is more electronegative than carbon.
TOPIC 08 • CARBOXYLIC ACIDS
Carboxylic Acids and Their Derivatives
Carboxylic acids contain the functional group −COOH and undergo a range of reactions useful in organic synthesis.
Properties
- Carboxylic acids are weak acids.
- They can form hydrogen bonds.
- They react with bases to form salts.
- They react with alcohols to form esters.
Esters
Hydrolysis
Esters can be hydrolysed under acidic or alkaline conditions.
Acyl Derivatives
The chemistry of acyl compounds involves nucleophilic substitution and is important in organic synthesis.
TOPIC 09 • ORGANIC SYNTHESIS
Organic Synthesis and Analysis
Organic synthesis involves converting one organic compound into another using appropriate reagents and conditions.
Reaction Pathways
- Identify the functional group being changed.
- Select an appropriate reagent.
- State suitable reaction conditions.
- Identify the organic product.
- Balance the equation where required.
NMR Spectroscopy
Nuclear magnetic resonance spectroscopy provides information about the chemical environment of nuclei within molecules.
- Number of signals
- Chemical shift
- Integration
- Splitting patterns
PRACTICAL SKILLS
Unit 4 Practical Chemistry
Practical knowledge is embedded throughout Unit 4 and can be assessed through written examination questions.
- Investigating reaction rates
- Measuring rates using experimental data
- Investigating equilibrium systems
- Acid–base titrations
- Organic preparations
- Qualitative observations
- Analysis and evaluation of experimental data
Be prepared to analyse experimental results, identify uncertainties and evaluate the reliability of conclusions.
EXAM PRACTICE
Unit 4 Mixed Practice
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It is the power to which the concentration of that reactant is raised in the experimentally determined rate equation.
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Increasing temperature and increasing concentration are two possible factors.
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A positive total entropy change indicates that the process is thermodynamically feasible.
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When a system at equilibrium is subjected to a change, the equilibrium position shifts in the direction that opposes the change.
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The aldehyde functional group is −CHO.
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It is a nucleophilic addition reaction.
QUICK REVIEW
Unit 4 Formula Vault
Connect equations, experimental evidence and chemical reasoning. In unfamiliar questions, identify what changes, determine what is being measured and justify every conclusion from the information provided.