CHEM1312H - Reaction Half-Lines

half-life (t_1/2) of a reaction

the time required for the concentration of a reactant to fall to ½ of its initial value

half-life of a first-order reaction

-t_1/2 = 0.693/k or t_1/2 = ln2/k (ln2 = 0.693)

-for the first-order reaction, t_1/2 is independent of the initial concentration

-a constant half-life is unique to first-order reactions

half-life of a second-order reaction

-t_1/2 = 1/k[A]₀

-for a second-order reaction, the half-life depends on the initial concentration

-the half-life continues to get longer as the concentration decreases

half-life of a zero-order reaction

-t_1/2 = [A]₀/2k

-for a zero-order reaction, the half-life depends on the initial concentration

-the half-life gets shorter as the concentration decreases