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

Exam questions on Rate equations and orders of reaction

1. A technician studies the gas-phase reaction 2NO(g) + 2H₂(g) → N₂(g) + 2H₂O(g) at constant temperature. Experiments show that the rate equation is rate = k[NO]²[H₂].
   The concentration of NO is doubled and the concentration of H₂ is halved, with the temperature unchanged. Deduce the factor by which the rate changes.2 marks
2. Peroxodisulfate ions oxidise iodide ions: S₂O₈²⁻(aq) + 2I⁻(aq) → 2SO₄²⁻(aq) + I₂(aq). A student measures the initial rate of this reaction in three experiments 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⁻] = 0.020 mol dm⁻³, [I⁻] = 0.080 mol dm⁻³, initial rate = 4.8 × 10⁻⁶ mol dm⁻³ s⁻¹.
   Calculate the initial rate of the reaction at the same temperature when [S₂O₈²⁻] = 0.050 mol dm⁻³ and [I⁻] = 0.060 mol dm⁻³.2 marks
3. A reactant R decomposes in solution at constant temperature. Its concentration is 0.800 mol dm⁻³ at the start, 0.400 mol dm⁻³ after 120 s, 0.200 mol dm⁻³ after 240 s and 0.100 mol dm⁻³ after 360 s.
   Deduce the order of reaction with respect to R and justify your answer.3 marks