Amylase catalyses the breakdown of starch into sugars. Identical mixtures of starch solution and amylase solution are kept at 15 ∘C15\,^\circ\mathrm{C}15∘C and 30 ∘C30\,^\circ\mathrm{C}30∘C. The starch takes longer to break down at 15 ∘C15\,^\circ\mathrm{C}15∘C.
Which statement explains the longer time at 15 ∘C15\,^\circ\mathrm{C}15∘C?
Particles have less kinetic energy, so they collide less often and a smaller fraction of collisions is successful.
Particles have less kinetic energy, so they collide less often, but the same fraction of collisions is successful.
The lower temperature means there are fewer reactant particles in the same volume, so collisions happen less often.
Amylase is used up at the lower temperature, so less remains to catalyse the reaction.
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.