Besides the rate constant, what factors determine the rate in the rate law?

• A. Temperature
• B. Concentrations of the reactants raised to their orders
• C. Pressure
• D. Catalyst presence

Answer: (B)

The rate law tells us that the rate is the product of the rate constant and terms that involve the reactants’ concentrations raised to certain powers (the reaction orders). Besides the rate constant, the factors that determine the rate are precisely how much of each reactant is present and how strongly each one affects the rate, which is captured by those exponents. In other words, the rate depends on [A] raised to the order with respect to A, [B] raised to the order with respect to B, and so on. The exponents aren’t fixed by the overall equation; they’re determined experimentally for the specific reaction.

So, the factor besides the rate constant is the concentrations of the reactants and the reaction orders that specify how sensitive the rate is to each concentration. Temperature, pressure, and catalysts influence the rate by altering the rate constant or the mechanism, rather than appearing as separate, direct factors in the rate-law expression. For example, if the rate law is rate = k [A]^2 [B], doubling [A] increases the rate by a factor of four, showing clearly how the concentrations and their orders govern the rate.