Which statement about rate law exponents m and n is true?

Which statement about rate law exponents m and n is true?

• A. They are determined experimentally and may differ from stoichiometric coefficients.
• B. They must equal the stoichiometric coefficients.
• C. They depend only on temperature.
• D. They are always equal to one.

Answer: (D)

Rate law exponents m and n indicate how the rate responds to changes in the concentrations of each reactant. They are determined experimentally by measuring how the rate changes when you vary [A] and [B], and they do not have to match the stoichiometric coefficients from the balanced equation. In many reactions, the observed orders with respect to reactants are not the same as their coefficients and can even be fractional or zero, reflecting the actual mechanism that controls the rate. Temperature affects the rate constant through the Arrhenius relationship, but it does not fix the exponents; the exponents are empirical and can change if the mechanism changes with conditions. So the statement that exponents are determined experimentally and may differ from stoichiometric coefficients is the true idea. The notions that they must equal stoichiometric coefficients, depend only on temperature, or are always one do not align with how rate laws are determined.

Rate law exponents m and n indicate how the rate responds to changes in the concentrations of each reactant. They are determined experimentally by measuring how the rate changes when you vary [A] and [B], and they do not have to match the stoichiometric coefficients from the balanced equation. In many reactions, the observed orders with respect to reactants are not the same as their coefficients and can even be fractional or zero, reflecting the actual mechanism that controls the rate. Temperature affects the rate constant through the Arrhenius relationship, but it does not fix the exponents; the exponents are empirical and can change if the mechanism changes with conditions. So the statement that exponents are determined experimentally and may differ from stoichiometric coefficients is the true idea. The notions that they must equal stoichiometric coefficients, depend only on temperature, or are always one do not align with how rate laws are determined.