Here, [A] and [B] are the molar concentrations of the reactants, k is the rate constant, and m and n are the reaction orders with respect to A and B. The value of k is specific to a reaction at a particular temperature. It does not depend on reactant concentrations, although it can change when temperature changes.
The exponents are not necessarily the coefficients in the balanced chemical equation. Rate-law exponents and the rate constant are found experimentally by observing how the rate changes when concentrations change.
All flashcards
What is a rate law?
A mathematical expression that relates a reaction rate to the concentrations of reactants, using a rate constant and reaction-order exponents.
What is the rate constant?
The proportionality constant in a rate law. For a given reaction it is independent of reactant concentrations, but its value can vary with temperature.
What does reaction order with respect to A mean?
It is the exponent of [A] in the rate law and describes how the rate depends on A's concentration when other conditions are held constant.
How is overall reaction order calculated?
Add the exponents of all reactant concentration terms in the rate law. For rate=k[A][B]2, the overall order is 3.
What does a zero-order reactant term mean?
Its concentration is raised to the zero power, so that term equals 1 and changing that reactant's concentration does not affect the rate under the stated conditions.
Quiz questions
What information does a chemical rate law express?Answer: How reaction rate depends on reactant concentrations.
For rate=k[A]m[B]n, what does m denote?Answer: The order with respect to reactant A.
For rate=k[A][B]2, what is the overall reaction order?Answer: Third order overall.
For rate=k[NO2]2[CO]0, what happens to the rate if [CO] changes while other conditions remain fixed?Answer: It remains unchanged under the stated conditions.
Why can rate-law exponents generally not be inferred from a balanced overall equation?Answer: They describe experimentally measured concentration dependences.
Based on Chemistry 2e by Paul Flowers, Klaus Theopold, Richard Langley, William R. Robinson, PhD (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.