What is the process used to determine the form of the rate law and the powers for each reactant?

• A. Determining a rate law
• B. Integrated rate law
• C. Energy diagram
• D. Reaction intermediate

Answer: (A)

Determining how the rate depends on reactant concentrations is done by establishing the rate law through experiments that reveal the reaction orders for each reactant. The rate law has the form rate = k [A]^m [B]^n ..., where m and n are the powers showing how sensitive the rate is to each concentration. These exponents are found experimentally by varying one reactant at a time and measuring initial rates (or using methods that fit rate data) to see how the rate changes. If doubling a reactant doubles the rate, that reactant is first order (exponent 1); if changing its concentration has little effect, it’s zero order, and so on. The integrated rate law, energy diagrams, and identification of intermediates serve different purposes: the integrated rate law relates concentration to time and helps determine the overall order, the energy diagram shows activation energy and energy changes, and an intermediate is a species in the mechanism—not the method for finding the rate law’s form and powers.