The initial concentration of reactant in a first-order reaction is 0.27 M. The rate constant for the reaction is 0.75 s−1. What is the concentration (mol/L) of reactant after 1.3 s? The initial concentration of reactant in a first-order reaction is 0.27 . The rate constant for the reaction is 0.75 . What is the concentration () of reactant after 1.3 ? 0.72 0.10 2.5 0.029 1.7