Which term describes the exponent to which a reactant concentration is raised in the rate law?

• A. Endothermic
• B. Reaction order
• C. Energy diagram
• D. Catalyst

Answer: (B)

The exponent to which a reactant concentration is raised in the rate law is the reaction order with respect to that reactant. In a rate law like rate = k[A]^m[B]^n, the numbers m and n are the orders for A and B, respectively, and they tell you how sensitive the rate is to changes in each concentration. The overall rate order is the sum m + n.

This order is determined experimentally and does not have to match the stoichiometric coefficients in the balanced equation. For example, if the rate law is rate = k[A]^2[B], A is second order and B is first order, giving a total order of three.

Other terms describe different ideas: endothermic refers to heat absorption, energy diagrams map energy changes during a reaction, and a catalyst speeds up a reaction by providing an alternative pathway (often lowering activation energy) without necessarily changing the meaning of the rate law's exponents.