Free Half-Life Calculator (First Order)
Calculate the half-life of a first-order reaction from its rate constant, or find the rate constant from a known half-life.
Half-Life (t½)
13.8629 s
Half-Life (t½) vs Rate Constant (k)
First-Order Half-Life
For a first-order reaction, the half-life is the time required for the concentration to decrease to half of its initial value. Uniquely for first-order kinetics, the half-life is independent of initial concentration.
Formula
t½ = ln(2) / k = 0.693 / k
where k is the first-order rate constant. This formula applies to radioactive decay, drug metabolism, and many chemical decomposition reactions.
Example Calculation
A first-order reaction with rate constant k = 0.05 s⁻¹.
- 01t½ = ln(2) / 0.05
- 02t½ = 0.6931 / 0.05 = 13.86 s
- 03In minutes: 13.86 / 60 = 0.231 min
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