EXERCISE A A scientist needs to calculate the rate constant, k, for a reaction known to be first order. The initial concentration of the reactar was 9.1 x 104 M, and after 345.0 s the concentration had dropped to 1.3 * 10M Calculate the rate constant for this reaction. Units Unrounded Value Rounded Value 30 EXERCISE B A scientist needed to calculate the rate constant, k, for a reaction known to be first order. The initial concentration of the reactant was 0.018 M, and after 630.0 s the concentration had dropped to 4.5 * 10 M. Calculate the rate constant for this reaction. Units Unrounded Value Rounded Value 12