Chemistry study notes
Reaction Kinetics
Extract a rate law from data, test a mechanism, and explain how conditions and catalysts change reaction speed.
A-Level 9476 (2026-2027)
Choose a topic
5 topicsRates, orders and rate constants
Read changing concentrations and compare controlled initial-rate experiments.
Concentration-time graphs and half-life
Recognise constant loss versus a constant fraction lost.
Test a mechanism and design a measurement
Connect elementary steps with observable rates and suitable signals.
Collisions, activation energy and temperature
Separate collision frequency from the fraction energetic enough to react.
Catalytic cycles, surfaces and enzymes
Follow regeneration of the catalyst in all four specified examples.
Scope and references
Learning outcomes and sources
8. Reaction Kinetics. Use the outcome map to find the explanation for a particular syllabus requirement.
See the learning outcome map
8(a) Explain the central kinetic terms.
- Rate, rate equation, order, rate constant
- Half-life
- Rate-determining step
- Activation energy
- Catalysis
A rate measures change per unit timeZero order loses equal amounts; first order loses equal fractionsA mechanism must match both the overall equation and the rate lawReaction needs both encounters and sufficient energyA catalyst supplies another mechanism
8(b) Construct and use simple rate equations.
- Orders 0, 1 or 2 for a species
- (i) Initial-rate deduction
- (ii) Zero/first-order concentration-time graphs
- (iii) Check a proposed mechanism
- (iv) Predict order from a mechanism
- (v) Calculate an initial rate from concentrations
- No integrated rate equations required
A rate measures change per unit timeCompare experiments that isolate one concentrationZero order loses equal amounts; first order loses equal fractionsA mechanism must match both the overall equation and the rate law
8(c) Understand and use first-order half-life.
- (i) Independence from concentration
- (ii) Half-life calculations
Zero order loses equal amounts; first order loses equal fractions
8(d) Calculate a rate constant from initial-rate data.
- Substitute experimental rate and concentrations
- Derive units from overall order
8(e) Devise a suitable rate experiment.
- Select a measurable signal from supplied reaction information
- Control conditions and identify measurement limitations
8(f) Explain concentration effects through collision frequency.
- More particles per volume
- Distinguish concentration from temperature effects
8(g) Explain activation energy using a Boltzmann distribution.
- Energy threshold
- Area representing the energetic fraction
8(h) Explain temperature effects on k and rate.
- Boltzmann distribution
- Collision frequency
- Activation energy unchanged for the same pathway
8(i) Explain catalytic lowering of a reaction barrier.
- (i) Different mechanism, lower activation energy, larger k
- (ii) Larger energetic fraction in the unchanged distribution
8(j) Outline homogeneous and heterogeneous catalytic action.
- (i) Haber process
- (ii) Vehicle-exhaust nitrogen-oxide removal
- (iii) Atmospheric NOx catalysis of SO2 oxidation
- (iv) Fe2+ catalysis of I-/S2O8^2-
- Catalyst regeneration and phase distinction
A homogeneous catalyst reacts through a regenerated intermediateA solid surface brings adsorbed reactants into a more reactive arrangement
8(k) Describe enzymes and their sensitivities.
- Protein biological catalysts
- Reaction and substrate specificity
- Lock-and-key model
- Temperature and pH sensitivity
- Protein structural levels and denaturation details not required
- SEAB H2 Chemistry 9476, examination 2026
Topic 8, printed pages 20-21. All 11 outcomes and every nested rate-law, catalyst and enzyme requirement inspected.