Which term refers to the equation that relates reaction rate to the concentrations of reactants?

• A. Rate Law
• B. Activation energy
• C. Half-life
• D. Catalyst

Answer: (A)

The rate law expresses how fast a reaction proceeds as a function of reactant concentrations. It’s an equation of the form rate = k [A]^m [B]^n ..., where k is the rate constant and m and n are the reaction orders with respect to each reactant. These exponents are determined experimentally and tell you how sensitive the rate is to changes in each concentration. For example, if the rate is first order in a reactant, doubling its concentration doubles the rate; if it’s second order in a reactant, doubling the concentration increases the rate by a factor of four. Activation energy is the energy barrier for the reaction, not the rate-law relation; half-life pertains to the time needed for the concentration to drop to half and depends on the rate law; a catalyst speeds up the reaction by lowering the activation energy, not by changing the form of the rate law.