5.3.A—Identify the rate law expression of a chemical reaction using data that show how the concentrations of reaction…

Identify the rate law expression of a chemical reaction using data that show how the concentrations of reaction species change over time. Kinetics UNIT 5

• The order of a reaction can be inferred from a graph of concentration of reactant versus time.
• If a reaction is first order with respect to a reactant being monitored, a plot of the natural log (ln) of the reactant concentration as a function of time will be linear.
• If a reaction is second order with respect to a reactant being monitored, a plot of the reciprocal of the concentration of that reactant versus time will be linear.
• The slopes of the concentration versus time data for zeroth, first, and second order reactions can be used to determine the rate constant for the reaction. Zeroth order: EQN: [A]t − [A]0 = −kt First order: EQN: ln[A]t − ln[A]0 = −kt Second order: EQN: 1/[A]t − 1/[A]0 = kt
• Half-life is a critical parameter for first order reactions because the half-life is constant and related to the rate constant for the reaction by the equation: EQN: t1/2 = 0.693/k.
• Radioactive decay processes provide an important illustration of first order kinetics.