A student investigated the reaction between solid sodium hydrogencarbonate and citric acid solution. The mass of sodium hydrogencarbonate was the same in every test.
For one test, the student added water to a fixed volume of the citric acid solution before starting the reaction. The diluted solution reacted more slowly than the undiluted solution.
Explain why dilution reduced the rate of reaction.
For another test, the student cooled both reactants before mixing them. The reaction was slower than when the reactants were at room temperature.
Explain why cooling reduced the rate of reaction.
127 exam-style questions on AQA GCSE Chemistry 6.1 Rate of reaction, covering 6.1.1a Calculating rates of reactions, 6.1.1b Gradient of a tangent as rate, 6.1.2 Factors which affect the rates of chemical reactions, 6.1.3 Collision theory and activation energy, and 6.1.4 Catalysts. Each one has a worked solution and a mark scheme showing where the marks go.