Home / iGCSE Chemistry 0620 Extended – 6.2 Rate of reaction- Exam Style Questions Paper 2

iGCSE Chemistry 0620 Extended - 6.2 Rate of reaction- Exam Style Questions Paper 2- New Syllabus

iGCSE Chemistry MCQ (Extended) Paper 2 - All Chapters

Question

Aqueous sodium thiosulfate reacts with dilute hydrochloric acid to form a yellow precipitate of sulfur.

The precipitate forms more quickly when the reactants are heated.

Which statements explain this observation?

  1. The reacting particles collide more frequently.
  2. The collisions between reacting particles have more energy.
  3. The activation energy of the reaction is lower.

A. 1 and 2
B. 1 and 3
C. 1 only
D. 2 and 3

▶️ Answer/Explanation
Increasing temperature increases the kinetic energy of particles, which increases both the frequency of collisions and the energy of collisions. A greater proportion of collisions have energy greater than the activation energy. Activation energy itself is not lowered by temperature; it is lowered by catalysts.
✅ Answer: (A)

Question

Zinc reacts with dilute hydrochloric acid.

Which statement about the particles in the reaction is correct?

A. Increasing the concentration of dilute hydrochloric acid increases the collision rate but has no effect on the activation energy.
B. Increasing the concentration of dilute hydrochloric acid increases the collision rate and the activation energy.
C. Increasing the temperature of the reaction increases the activation energy.
D. Increasing the temperature of the reaction causes all collisions to lead to a reaction.

▶️ Answer/Explanation
Increasing concentration increases the number of particles per unit volume, which increases the frequency of collisions (collision rate). However, activation energy is a fixed energy barrier for a particular reaction and is not affected by changes in concentration or temperature. Only a catalyst can lower activation energy.
✅ Answer: (A)

Question

Which statement describes the effect of adding a catalyst to a chemical reaction?

A. The activation energy, Ea, of the reaction is increased.
B. The enthalpy change, ΔH, of the reaction stays unchanged.
C. The frequency of collisions between the particles is decreased.
D. The kinetic energy of the particles is increased.

▶️ Answer/Explanation
A catalyst provides an alternative reaction pathway with a lower activation energy, so option A is wrong. The enthalpy change (ΔH) depends only on the energy difference between reactants and products, which is not affected by a catalyst, so option B is correct. A catalyst does not change collision frequency or the kinetic energy of particles directly.
✅ Answer: (B)
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