Radioactive decay is a process that follows first-order kinetics. The half-life of 241Am is 432.2 years; how long (in minutes) would it take for the amount of 241Am to decrease to 52.47% of its initial amount? Key Concept: Half-life for first order reaction. t = 0.693/k. Strategy: Determine rate constant and then calculate time using integrated first order rate law.

For the reaction H2(g) + I2(g) 2 HI(g), the activation energy, Ea, is 166.0 kJ/mol, and k = 0.0002700 L/(mol*s) at 600.0 K. At what temperature (Kelvin scale) is k = 0.008659 L/(mol*s)? Key Concept: The Arrhenius equation, ln(k2/k1) = EA/R*[1/T1 - 1/T2], explains how the rate of a reaction changes with temperature. Generally, we expect the reaction rate (rate constant) to increase when the temperature increases. Solution: 1. Substitute all given quantities into the Arrhenius equation, making sure the activation energy is expressed in J/mol; use R = 8.3145 J/mol*K. 2. Solve for the unknown T.