The same volumes and concentrations of two solutions are mixed. The reaction mixture takes 120 s to reach a particular colour at 20 ∘C20\,^\circ\mathrm{C}20∘C and 30 s to reach the same colour at 40 ∘C40\,^\circ\mathrm{C}40∘C.
Which option explains the shorter time at 40 ∘C40\,^\circ\mathrm{C}40∘C?
Heating increases the surface area to volume ratio, so more reactant particles are exposed.
Heating raises the kinetic energy of the particles, so successful collisions occur more often each second.
Heating puts more reactant particles into the same volume, so collisions occur more often each second.
Heating provides an alternative pathway, so less energy is needed for the particles 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.