MCAT General Chemistry Question 63: Answer and Explanation

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Question: 63

3. A reactant in a second-order reaction at a certain temperature is increased by a factor of 4. By how much is the rate of the reaction altered?

  • A. It is unchanged.
  • B. It is increased by a factor of 4.
  • C. It is increased by a factor of 16.
  • D. It cannot be determined from the information given.

Correct Answer: D

Explanation:

A second-order reaction can be second-order with respect to one reactant, or first-order with respect to two different reactants. In this case, one reactant was increased by a factor of 4. If the reaction is second-order with respect to this reactant, the rate will increase by a factor of 16. If it is first-order with respect to this reactant (and first-order with respect to another reactant), the rate will increase by a factor of 4. We do not know which of these is this correct rate law and, thus, cannot determine the effect on the rate.

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