In the description of the rate law, which statement is true about rate, rate constant, and concentrations?

• A. The rate equals the rate constant times concentrations; rate constant depends on concentrations
• B. The rate is independent of concentrations
• C. The rate constant is unrelated to the rate
• D. The rate equals the rate constant times concentrations of the reactants raised to their orders; rate constant does not depend on concentrations

Answer: (D)

The rate law shows how the rate depends on the concentrations of the reactants through their reaction orders, with the rate proportional to the rate constant times the product of each concentration raised to its respective order. The rate constant k is a separate factor that does not vary with concentrations (it can change with temperature or mechanism, but not with how much reactant is present). So the statement that the rate equals k times the concentrations raised to the powers of their orders, and that the rate constant does not depend on concentrations, captures the essential relationship. This contrasts with ideas that the rate is independent of concentrations or that k is unrelated to the rate, which do not hold in general for rate laws.