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Question

Difficulty: MediumFactors Affecting Rates of Reaction

Which of the following changes will increase the rate of reaction between dilute hydrochloric acid and zinc dust primarily by increasing the number of reactant particles per unit volume, thereby increasing the frequency of effective collisions without altering the average kinetic energy of the molecules?

  1. Increasing the concentration of the hydrochloric acid solutionAnswer
  2. B
    Increasing the temperature of the reaction mixture
  3. C
    Adding a catalyst that shifts the equilibrium position toward the products
  4. D
    Replacing zinc dust with larger zinc granules of equal mass

Answer

Increasing the concentration of the hydrochloric acid solution
Increasing the concentration of hydrochloric acid increases the number of hydrogen ions (H+H^+) present per unit volume of solution. This increases the frequency of collisions between reactant particles without affecting their average kinetic energy or altering the activation energy of the reaction pathway.

Step-by-Step Solution

1
Analyze how concentration influences particle collision mechanics according to collision theory.
A higher concentration contains a greater number of solute particles (H+H^+ ions) per unit volume.
With more reactant particles crowded in the same volume, collision frequency increases.
2
Evaluate the energy condition specified in the stem.
Concentration changes do not alter particle speed or average kinetic energy, fulfilling the exact requirement.
Average kinetic energy is strictly dependent on temperature.

Key Concept

Effect of concentration on reaction rate via collision frequency
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Topics

Factors Affecting Rates of Reaction