Kinetics and Equilibrium Problem Solving

This lesson brings together kinetics and equilibrium in the kind of multi-step problems that appear in Edexcel A-level exams. We will work through extended calculations combining rate equations, the Arrhenius equation, ICE tables, and Kp calculations, building the fluency you need for the exam.

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Multi-Step Rate Equation Problems

Problem 1: Determining the Rate Equation and Calculating k

The reaction X + 2Y → Z was studied using the initial rate method:

Experiment	[X] / mol dm⁻³	[Y] / mol dm⁻³	Initial rate / mol dm⁻³ s⁻¹
1	0.10	0.10	3.2 × 10⁻³
2	0.10	0.20	1.28 × 10⁻²
3	0.20	0.10	6.4 × 10⁻³

Step 1: Determine order with respect to Y.

Compare Experiments 1 and 2 ([X] constant):

[Y] doubles (0.10 → 0.20). Rate changes: 1.28 × 10⁻² / 3.2 × 10⁻³ = 4.0 = 2²

Order with respect to Y = 2

Step 2: Determine order with respect to X.

Compare Experiments 1 and 3 ([Y] constant):