Half-life equation for first-order reactions: t1/2=0.693/k where t1/2 is the half-life in seconds , and k is the rate constant in inverse seconds . a.) What is the half-life of a first-order reaction with a rate constant of 6.10×10-4 s-1? b.) What is the rate constant of a first-order reaction that takes 539 seconds for the reactant concentration to drop to half of its initial value? c.) A certain first-order reaction has a rate constant of 1.00x10-3 s-1. How long will it take for the reactant concentration to drop to 1/8 of its initial value?