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Reviewed CSCA Chemistry question · Standard

For the exothermic reaction N2(g) + 3H2(g) ⇌ 2NH3(g), which change will increase the rate of the forward reaction without necessarily shifting the equilibrium position?

  1. Increasing the concentration of NH3
  2. Adding a catalyst
  3. Decreasing the pressure
  4. Increasing the temperature
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Correct answer

B. Adding a catalyst

Principle or equation

A catalyst provides an alternative reaction pathway with lower activation energy, increasing both forward and reverse reaction rates equally. It does not change the equilibrium position.

Why this answer is correct

Adding a catalyst speeds up the attainment of equilibrium by increasing the rate of both forward and reverse reactions, but it does not shift the equilibrium position. Increasing NH3 concentration shifts equilibrium left, decreasing pressure shifts toward more gas moles (left), and increasing temperature for an exothermic reaction shifts equilibrium left.

Example

In the Haber process, iron is used as a catalyst to increase the rate of ammonia production without affecting the equilibrium yield.

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