Rate Constant Calculator

The Rate Constant Calculator computes the rate constant $k$, reaction rate, half-life, or concentration for zero, first, and second-order reactions. The rate constant is a proportionality factor that describes how fast a reaction proceeds at a given temperature.

Rate laws by order:

Zero order: $\text{rate} = k$, $T_{1/2} = [A] / (2k)$
First order: $\text{rate} = k[A]$, $T_{1/2} = 0.693 / k$
Second order: $\text{rate} = k[A]^2$, $T_{1/2} = 1 / (k[A])$

Example: For a first-order reaction with $[\text{A}] = 0.5$ M and rate $= 0.035$ M/s, the rate constant is $k = 0.035 / 0.5 = 0.07$ s$^{-1}$.

Frequently Asked Questions

How do I find the rate constant?

For a first-order reaction, divide the rate by the concentration: $k = \text{rate} / [A]$. For zero order, $k$ equals the rate directly. For second order, $k = \text{rate} / [A]^2$.

What is half-life for a first-order reaction?

Half-life is $T_{1/2} = 0.693 / k$. It is independent of initial concentration, which is a hallmark of first-order kinetics.

What factors affect the rate constant?

Only temperature affects the rate constant. Changing initial concentration changes the rate but not $k$. Catalysts change the reaction pathway and thus the rate constant.

What units does k have?

Units depend on reaction order. Zero order: M/s. First order: 1/s. Second order: 1/(M·s). Always check that rate and concentration units are consistent.

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Rate Constant Calculator

Rate Constant Calculator

Frequently Asked Questions

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