2025 O Level Chem P1 Q33 — Rate of Reaction Solution
Question
The rate of three reactions is investigated by measuring the amount of carbon dioxide produced over time. Reaction X produces 18 moles of carbon dioxide in 2 hours. Reaction Y produces 18 dm³ of carbon dioxide in 2 minutes. Reaction Z produces 0.50 g of carbon dioxide in 2 seconds. All measurements are at room temperature and pressure. Which row is correct?
Correct answer: A
Video Solution
Explanation
Answer: A. Convert each reaction's rate to the same units (e.g., moles per second) to compare.
Reaction X: 18 mol / 2 h = 9 mol/h = \(2.5 \times 10^{-3}\) mol/s.
Reaction Y: 18 dm³ / 2 min at rtp = 9 dm³/min = 0.150 dm³/s = \(6.25 \times 10^{-3}\) mol/s (since 1 mol gas = 24 dm³ at rtp).
Reaction Z: 0.50 g / 2 s = 0.25 g/s = \(0.25/44 = 5.7 \times 10^{-3}\) mol/s.
Ranking: X (2.5e-3) < Z (5.7e-3) < Y (6.25e-3) mol/s. So X is the lowest and Y the highest → A.
Get the Sec 3 / Sec 4 recording package
Every O Level Pure Chemistry TYS MCQ solution video, plus full Sec 3 / Sec 4 topic recordings.
Find out more