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Difficulty: EasyFactors Affecting Rates of Reaction

During the laboratory preparation of oxygen gas, manganese(IV) oxide (MnO2(s)MnO_{2(s)}) is added to hydrogen peroxide solution (H2O2(aq)H_2O_{2(aq)}) to increase the speed of decomposition. Which of the following best explains how manganese(IV) oxide increases the rate of this reaction?

  1. It provides an alternative reaction pathway with a lower activation energy.Answer
  2. B
    It shifts the equilibrium position to yield a higher volume of oxygen gas.
  3. C
    It increases the average kinetic energy of the hydrogen peroxide molecules.
  4. D
    It increases the total concentration of the reacting hydrogen peroxide molecules.

Answer

Manganese(IV) oxide acts as a catalyst, increasing the rate of reaction by providing an alternative reaction pathway with a lower activation energy.
Adding a catalyst such as manganese(IV) oxide provides an alternative reaction pathway with a lower activation energy (EaE_a). As a result, a larger fraction of colliding reactant molecules possess energy equal to or greater than the activation energy threshold, leading to an increased frequency of effective collisions.

Step-by-Step Solution

1
Identify the role of manganese(IV) oxide in the decomposition of hydrogen peroxide.
Manganese(IV) oxide is a catalyst because it speeds up the reaction without being consumed.
Recognizing the function of the added chemical substance is the essential first step.
2
Apply Collision Theory to explain catalyst activity.
Catalysts provide a lower activation energy route.
Lowering activation energy allows a greater proportion of molecular collisions to have sufficient energy to react per unit time.

Key Concept

Effect of catalysts on reaction rate and activation energy
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Topics

Factors Affecting Rates of Reaction