Collision theory, concentration and pressureAQA A-Level Chemistry: Mind map

Exam questions on Collision theory, concentration and pressure

1. A student investigates the reaction between marble chips (calcium carbonate, in excess) and 50.0 cm³ of hydrochloric acid, CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g), by measuring the volume of carbon dioxide produced using a gas syringe. She repeats the experiment using 2.0 mol dm⁻³ acid in place of 1.0 mol dm⁻³ acid. All other conditions, including the temperature and the mass and size of the marble chips, are kept the same.
   Explain why most collisions between particles do not lead to a reaction.2 marks
2. Nitrogen monoxide reacts with oxygen in the gas phase at constant temperature: 2NO(g) + O₂(g) → 2NO₂(g). A mixture of the gases is held in a sealed cylinder fitted with a movable piston.
   Explain, in terms of particles, why halving the volume of the cylinder increases the rate of reaction.2 marks
3. A student investigates how concentration affects the rate of the reaction between sodium thiosulfate and hydrochloric acid: Na₂S₂O₃(aq) + 2HCl(aq) → 2NaCl(aq) + S(s) + SO₂(g) + H₂O(l). In each experiment 5.0 cm³ of 1.0 mol dm⁻³ hydrochloric acid is added to the thiosulfate solution at 20 °C, and the time taken for a cross viewed through the mixture to disappear is measured. Experiment 1 uses 50.0 cm³ of 0.20 mol dm⁻³ sodium thiosulfate solution and takes 36 s. Experiment 2 uses 25.0 cm³ of 0.20 mol dm⁻³ sodium thiosulfate solution mixed with 25.0 cm³ of water, and takes 72 s.
   Explain, in terms of collisions, why the cross disappears more slowly in experiment 2.3 marks