Intermediate Topic 424 of 1102 Kinetics & Equilibrium
Rate Constant
The proportionality constant k in the rate law, depending on temperature and catalyst.
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In-depth explanation of Rate Constant
The rate constant k is the proportionality constant in the rate law that links the rate to reactant concentrations. It is specific to a given reaction at a given temperature and does not depend on the concentrations themselves. Its units depend on the overall order: for a first order reaction k has units of s^-1, while for a second order reaction it has units of L mol^-1 s^-1. Larger values of k correspond to faster reactions, and k increases strongly with temperature according to the Arrhenius equation. A catalyst also changes k by providing a route with lower activation energy.
Going deeper: Rate Constant
Key ideas: Always derive the units from the overall order n: units of k = (concentration)^(1-n) per time, so zero order is mol per L per s, first order is per s, second order is L per mol per s. Compare rate constants only at the same temperature and for the same rate law form. Use ln k plots against 1/T to extract activation energy.
Common mistakes and connections: Students quote k for a reaction without units or temperature, which makes it meaningless. Another error is thinking k depends on concentration, when only the rate does. Also remember k depends on how the rate is defined, so a rate written per mole of a species with coefficient 2 gives a k that differs by a factor of 2. See the Arrhenius equation for the temperature link.
Visualization of Rate Constant
A larger k means faster decay. With k = 0.0231 per minute the concentration halves every 30 minutes, whatever the starting amount. The interactive lesson shows this as a live animation or chart.
Worked example and use case
A first order reaction with k = 0.0231 min^-1 has a half-life of 0.693/0.0231 = 30.0 minutes.
Frequently asked questions about Rate Constant
What is Rate Constant?
The proportionality constant k in the rate law, depending on temperature and catalyst.
Is Rate Constant a beginner, intermediate or advanced topic?
Rate Constant is a intermediate topic in Kinetics & Equilibrium. It builds on the vocabulary of beginner topics in this area.
What should I learn before Rate Constant?
Study these earlier topics in Kinetics & Equilibrium first: Reaction Rate, Average and Instantaneous Rate, Rate Law.
What comes after Rate Constant?
The next topics in Kinetics & Equilibrium are Order of Reaction and Zero Order Reaction.
Can I practise Rate Constant with quizzes?
Yes. The interactive lesson includes a self-check question on Rate Constant, and the Kinetics & Equilibrium quiz draws on every topic in this area.
Where Rate Constant fits in Kinetics & Equilibrium
Rate Constant is topic 5 of 91 in Kinetics & Equilibrium.