Collision theory and rates of reactionEdexcel International A Level Chemistry: Mind map

Exam questions on Collision theory and rates of reaction

1. A student investigates the reaction between sodium thiosulfate solution and dilute hydrochloric acid, which forms a fine yellow precipitate of sulfur. She places the reaction flask on a printed cross and measures the time taken for the cross to disappear when viewed from above.
   At a higher temperature the cross disappears after 22 s. Calculate the relative rate (1 ÷ time) at each temperature and the factor by which the rate has increased.2 marks
2. Marble chips (calcium carbonate) are added to excess dilute hydrochloric acid in a conical flask on a balance. Carbon dioxide escapes, so the mass of the flask and contents falls as the reaction proceeds.
   The reaction is repeated at a higher temperature. Explain, using collision theory, why the rate increases.2 marks
3. A student reacts excess magnesium ribbon with 50 cm³ of dilute sulfuric acid and collects the hydrogen in a gas syringe. She plots the volume of gas against time and draws tangents to the curve.
   Explain, using collision theory, why the gradient of the graph decreases as the reaction proceeds.3 marks