First-Order Rate Law

• Order = 1 → changing the reactant concentration has an identical effect on the reaction rate (same factor)
• Rate Law =
•  If a plot of ln[A] versus time is a straight line → reaction is first order
• Integrated First Order rate law: (on reference sheet)
• Value of k: k = – (slope of plot)

Half-Life of a First-Order Reaction

• Half life: the time required for a reactant to reach half its original concentration (on RFS)
• The half-life of a 1st-order reaction is only dependent on K (NOT on concentration)

○ A constant time is required to reduce the concentration of the reactant by half, and then by half again

■ All type of radioactive decay is first-order

• Can find k if given a graph of time and concentration by using half-life.

Second-Order Reaction

• Order = 2 → changing reactant concentration will affect the reaction rate to the square of the change in the reactant
•  Rate Law: Rate =
• Value of k: k = (slope of plot)
• Integrated Rate Law: (on ref. sheet)
•  If a plot of 1/[A] versus time is a straight line → reaction is second order

Half-Life of a Second Order Reaction

• (not on RFS)
• The half-life of a second-order reaction depends on both K and the initial concentration [A]₀
• To find half-life must be given value of k

Zero-Order Rate Law

• Order = 0 → a change in reactant concentration has no effect on the rate
• Reactant will not appear in the rate law for the reaction
• Rate Law: Rate = k
• Value of k: k = – (slope of plot)
• Integrated rate law is:
•  If a plot of [reactant] versus time is a straight line → reaction is zero-order