For a first-order reaction, the half-life is constant. It depends only on the rate constant and not on the reactant concentration. It is expressed as: t1/2 0.693/k. For a second order reation, the half-life depends on the rate constant and the concentration of the reactant and so is expressed as: t1/2=1/k[A]0.
a.) A certain first-order reaction (A---> products) has a rate constant of 6.00×10?3 s-1 at 45 degrees C. How many minutes does it take for the concentration of the reactant, [A], to drop to 6.25% of the original concentration?
B.) A certain second-order reaction (B---> products) has a rate constant of 1.70×10?3 at 27 degrees C and an initial half-life of 288s. What is the concentration of the reactant B after one half-life?