3. Rate of Reactions

Question 1

Factors affecting rate of reaction

7 factors

Answer 1

1. Effect of particle size (of solid reactant)
2. Effect of concentration (of solution)
3. Effect of basicity (of acid)
4. Effect of strength (of acid/alkali)
5. Effect of pressure (of gaseous reactant)
6. Effect of temperature (of reaction mixture)
7. Effect of catalyst (being present or not)

Question 2

Effect of particle size (of solid reactant)

Explanation in terms of collision between reacting particles

Answer 2

1. When the particle size of a reactant decreases, the total surface area of the reactant increases.
2. There is a larger total surface area exposed for the other reacting particles to collide with at any one time.
3. Hence, the frequency of effective collisions between reacting particles increases, and the rate of reaction increases.

Question 3

Effect of Concentration (of solution)

Explanation in terms of collision between reacting particles

Answer 3

1. When the concentration of a reactant increases, the number of reacting particles per unit volume increases.
2. Hence, the frequency of effective collisions between reacting particles increases, and the rate of reaction increases.

Question 4

Effect of basicity (of acid)

Explanation in terms of collision between reacting particles

Answer 4

1. Sulfuric acid is a dibasic acid and hydrochloric acid is a monobasic acid.
2. For the same concentration of acid, the concentration of hydrogen ions in sulfuric acid is twice the concentration of hydrogen ions in hydrochloric acid.
3. When the concentration of hydrogen ions increases, the number of hydrogen ions per unit volume increases.
4. Hence, the frequency of effective collisions between reacting particles increases, and the rate of reaction increases.

Question 5

Effect of strength (of acid/alkali)

Explanation in terms of collision between reacting particles

Answer 5

1. Hydrochloric acid is a strong acid which completely dissociates in water/aqueous solution to form hydrogen ions.
2. Aqueous ethanoic acid is a weak acid which partially dissociates in water/aqueous solution to form hydrogen ions.
3. For the same concentration of acid, the concentration of hydrogen ions in hydrochloric acid is higher than the concentration of hydrogen ions in aqueous ethanoic acid.
4. When the concentration of hydrogen ions increases, the number of hydrogen ions per unit volume increases.
5. Hence, the frequency of effective collisions between reacting particles increases, and the rate of reaction increases.

Question 6

Effect of pressure (of gaseous reactant)

Explanation in terms of collision between reacting particles

Answer 6

1. When the pressure of a reaction mixture involving gaseous reactants increases, the number of reacting particles per unit volume increases.
2. Hence, the frequency of effective collisions between reacting particles increases, and the rate of reaction increases.

Question 7

Effect of temperature (of reaction mixture)

Explanation in terms of collision between reacting particles

Answer 7

1. When the temperature of the reaction mixture increases, the reacting particles will gain kinetic energy and move faster.
2. When the temperature of the reaction mixture increases, the number of reacting particles with energy equal to or more than the activation energy increases.
3. Hence, the frequency of effective collisions between reacting particles increases, and the rate of reaction increases.

Question 8

Effect of catalyst (being present or not)

Explanation in terms of collision between reacting particles

Answer 8

A catalyst is a substance that increases the rate of chemical reactions without being chemically changed at the end of the reaction.

1. A catalyst provides an alternative pathway with a lower activation energy for the reaction to occur.
2. The number of reacting particles with energy equal to or more than the activation energy increases.
3. Hence, the frequency of effective collisions between reacting particles increases, and the rate of reaction increases in the presence of a catalyst.