In the rate law, what does the exponent indicate?

• A. The exponent equals the stoichiometric coefficient
• B. The exponent equals the reaction order with respect to that reactant
• C. The exponent is always 0 or 1
• D. The exponent is irrelevant to rate law

Answer: (B)

The rate law shows how fast a reaction goes as a function of each reactant’s concentration, and the exponent in front of a reactant’s concentration is the reaction order with respect to that reactant. This order is determined experimentally and need not match the stoichiometric coefficient from the balanced equation. That’s why the exponent tells you how strongly the rate depends on that reactant’s concentration.

So the exponent being the reaction order with respect to that reactant is the right interpretation. The other statements aren’t generally true: exponents don’t have to match stoichiometric coefficients, they aren’t restricted to 0 or 1, and they’re not irrelevant to the rate law.