In the rate law Rate = k [A]^m [B]^n, which factor does not directly affect the numerical value of the rate constant k?

• A. Temperature
• B. Catalyst
• C. Concentration of A
• D. The reaction order with respect to A

Answer: (C)

The rate constant k is an intrinsic property that depends on temperature and the presence of a catalyst (and the reaction mechanism), not on how much reactant is present. In the rate law, the concentrations of A and B appear as [A]^m and [B]^n, which determine how sensitive the rate is to those concentrations. Changing [A] changes the observed rate by a factor of [A]^m, but it does not change the numerical value of k itself. Temperature increases k via the Arrhenius relationship, and a catalyst provides a faster pathway that also increases k. So the concentration of A does not directly affect the value of k.