Half-Life of a Reaction
The time required for the concentration of a reactant to fall to half its initial value.
Formula / equation
t½ = 0.693 / k (first order)
Unit
s
In depth
The way half-life depends on starting concentration identifies the order at a glance: it is constant for first order, proportional to concentration for zero order, and inversely proportional for second order. First-order half-lives are especially useful because they are independent of the amount present.
Examples in the real world
A first-order rate constant of 0.0347 min⁻¹ gives a half-life of 20 minutes at any starting concentration.