Rate equations and orders of reactionEdexcel A-Level Chemistry: Mind map

Exam questions on Rate equations and orders of reaction

1. The reaction between peroxodisulfate ions and iodide ions is S₂O₈²⁻(aq) + 2I⁻(aq) → 2SO₄²⁻(aq) + I₂(aq). Initial rates were measured at constant temperature. Experiment 1: [S₂O₈²⁻] = 0.020 mol dm⁻³, [I⁻] = 0.040 mol dm⁻³, initial rate = 2.4 × 10⁻⁶ mol dm⁻³ s⁻¹. Experiment 2: [S₂O₈²⁻] = 0.040 mol dm⁻³, [I⁻] = 0.040 mol dm⁻³, initial rate = 4.8 × 10⁻⁶ mol dm⁻³ s⁻¹. Experiment 3: [S₂O₈²⁻] = 0.040 mol dm⁻³, [I⁻] = 0.080 mol dm⁻³, initial rate = 9.6 × 10⁻⁶ mol dm⁻³ s⁻¹.
   Calculate the value of the rate constant, k, for this reaction, including its units.2 marks
2. Dinitrogen pentoxide, N₂O₅, decomposes in solution at constant temperature. The initial concentration of N₂O₅ is 0.80 mol dm⁻³. It falls to 0.40 mol dm⁻³ after 120 s and to 0.20 mol dm⁻³ after a further 120 s. The rate constant for the reaction at this temperature is 5.78 × 10⁻³ s⁻¹.
   Calculate the initial rate of reaction, including units.2 marks
3. Nitrogen monoxide reacts with hydrogen: 2NO(g) + 2H₂(g) → N₂(g) + 2H₂O(g). Initial rates were measured at constant temperature. Experiment 1: [NO] = 0.010 mol dm⁻³, [H₂] = 0.010 mol dm⁻³, initial rate = 2.0 × 10⁻⁷ mol dm⁻³ s⁻¹. Experiment 2: [NO] = 0.020 mol dm⁻³, [H₂] = 0.010 mol dm⁻³, initial rate = 8.0 × 10⁻⁷ mol dm⁻³ s⁻¹. Experiment 3: [NO] = 0.010 mol dm⁻³, [H₂] = 0.030 mol dm⁻³, initial rate = 6.0 × 10⁻⁷ mol dm⁻³ s⁻¹.
   Use the data to deduce the order of reaction with respect to NO and with respect to H₂, and write the rate equation.3 marks