A reaction is represented by the equation A+B→C\text{A} + \text{B} \rightarrow \text{C}A+B→C. A small amount of substance X is added. The reaction becomes faster, and the mass of X is the same at the end as at the start.
Explain why X is not included in the equation and how X increases 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.