The rate constant, k, for a first-order reaction is equal to 4.3 × 10-4 s-1. What is the half-life for the reaction? The rate constant, k, for a first-order reaction is equal to 4.3 × 10-4 s-1. What is the half-life for the reaction? 1.9 × 103 s 1.2 × 103 s 1.6 × 103 s 3.0 × 10-4 s