MCAT Math Question 14: Answer and Explanation
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Question: 14
14. The rate of a reaction is calculated as a change in concentration per time. What are the units of the rate constant, k, in a reaction that is second order overall with respect to one species? (Note: A second-order reaction of this type has a rate law with the form rate = k[A]2, where [A] is the concentration of the species.)
- A.
- B.
- C.
- D.
Correct Answer: C
Explanation:
According to the question stem, the rate of a reaction is measured as a change in concentration over time, and thus has the units 
where M (molarity) is measured in moles per liter. However, the rate of the reaction is equal to a rate constant times the concentrations of certain reactants squared. In this case, we know the units of everything except the rate constant and must solve for its units:
