Which statement best describes the rate constant?

• A. It is a measure of intrinsic reactivity and is experimentally determined
• B. It depends on temperature
• C. It is the same as the rate
• D. It is unrelated to the rate law

Answer: (A)

The rate constant is the proportionality factor that links the rate to the concentrations in the rate law; it encodes the inherent speed of the reaction at a given temperature. Because it reflects intrinsic reactivity, k is determined experimentally by measuring how fast the reaction proceeds for known concentrations and solving for k from the rate law. It is not the same as the rate itself, and it is a part of the rate law, not something unrelated to it. Note that k does depend on temperature (it changes if you heat or cool the system), but at a fixed temperature its value captures how readily the reaction occurs, independent of concentrations.