The half-life of a first-order reaction is 10 minutes. What fraction of the reactant remains after 30 minutes?
Correct: C
For a first-order reaction, the half-life (t1/2) is constant and independent of the initial concentration. If the half-life is 10 minutes, then after 10 minutes, 1/2 of the reactant remains. After another 10 minutes (20 minutes total), 1/2 of the remaining 1/2, or 1/4, remains. After another 10 minutes (30 minutes total), 1/2 of the remaining 1/4, or 1/8, remains.