rates of reactions

reaction rate

change in concentration over time

rate law

describes how the concentration changes are a reaction progresses

• greater concentrations generally → higher reaction rate

  • more collisions

differential rate laws

mathematical relationship between reaction rate and the concentration of reactants

• rate constant - k - unique for a particular temp - M^(1-n)/s

• reaction order - exponent of the concentration n

zero order reactions

• rate of concentration does not change with the concentration of reactants

  • reaction rate is constant

  • M/s

first order reactions

• rate of reaction is directly proportional to reactant concentration

• as reaction proceeds, rate will decrease b/c reactant concentration decreases

• 1/s

second order reactions

• rate of reaction is directly proportional to the square of the reactant concentration

• rate is much more sensitive to reactant concentration

• 1/M*s

method of initial rates

same reaction run multiple times, varying concentration of reactants systematically

• initial rate of reaction measured for each experiment/trial

integrated rate law

• describes the relationship between the concentrations of the reactants and time

zeroth-order integrated rate laws

• rate is proportional to a constant

• k[A]⁰ = k = -dA/dt

• [A]_t = -kt + [A]₀

first-order integrated rate laws

• rate is proportional to the concentration of A

• rate = k[A] = -dA/dt

• ln[At] = -kt + ln[A]₀ OR ln[A]_t/[A]₀ = -kt

  • At = concentration of A at any time t

  • A0 = initial concentration of A

  • k = rate constant

second-order integrated rate laws

• rate = k[A]² = -dA/dt

• 1/[A]_t = kt + 1/[A]₀

  • At = concentration of A at any time t

  • A0 = initial concentration of A

  • k = rate constant