Candidates should be able to:

Rate graphs and orders

1. explain and use the terms: rate of reaction, order, rate constant, half-life, rate determining step;
2. deduce, from a concentration-time graph, the rate of a reaction and the half-life of a first order reaction;
3. state that the half-life of a first-order reaction is independent of the concentration;
4. deduce, from a rate-concentration graph, the order (0, 1 or 2) with respect to a reactant;
5. determine, using the initial rates method, the order (0, 1 or 2) with respect to a reactant;

Rate equations; rate constant

6. deduce, from orders, a rate equation of the form: rate = k[A]^m[B]ⁿ for which m and n are 0, 1 or 2;
7. calculate the rate constant, k, from a rate equation;
8. explain qualitatively the effect of temperature change on a rate constant and hence the rate of a reaction;

Practical Skills

• Continuous monitoring of a reaction for 'quantity' against time graph: CaCO₃/HCl: monitoring gas or mass loss; H⁺/I₂/ (CH₃)₂CO: monitoring [I₂] using a colorimeter .
• Clock reactions for determination of orders and rate constants by initial rates and rate concentration graphs: Iodine clocks: I₂/S₂O₈^2- or H⁺/H₂O₂/I₂ with S₂O₃ ^2- (or vitamin C); Thiosulfate clock: HCl/S₂O₃ ^2-.
• The effect of temperature on reaction rates (clock reactions above are suitable).

IODINATION OF PROPANONE

IODINE CLOCK REACTION

THIOSULPHATE/ACID REACTION