A student times how long it takes for a cross under a flask to disappear when sodium thiosulfate solution reacts with dilute hydrochloric acid. The student repeats the experiment at the same temperature with a more concentrated sodium thiosulfate solution. The cross disappears sooner.
Why is the rate of reaction greater with the more concentrated solution?
There are more thiosulfate particles in the same volume, so collisions are more frequent.
There are more thiosulfate particles in the same volume, so a greater fraction of collisions succeed.
The particles have more kinetic energy, so they collide more often and with more energy.
The activation energy is lower, so more of the collisions have enough energy to react.
122 exam-style questions on OCR GCSE Chemistry 5.2 Controlling reactions, covering 5.2.1 Measuring and interpreting rate of reaction, 5.2.2 Factors affecting rate and collision theory, and 5.2.3 Catalysts, activation energy and enzymes. Each one has a worked solution and a mark scheme showing where the marks go.