How do you find rate law for a reaction?
You do a series of experiments to determine how the rate depends on the concentration of each component in the reaction.
For a reaction aA +bB → products, the rate law is
You must determine the values of
One way is to use initial concentrations. It is called the method of initial rates.
Find the rate law for the reaction aA +bB → products at 27 °C, given the data below.
Trial; [A]₀; [B]₀; rate
1; 1.0 mol·L⁻¹; 1.0 mol·L⁻¹; 2.0 mol·L⁻¹s⁻¹
2: 1.0 mol·L⁻¹; 2.0 mol·L⁻¹; 8.1 mol·L⁻¹s⁻¹
3; 2.0 mol·L⁻¹; 2.0 mol·L⁻¹; 15.9 mol·L⁻¹s⁻¹
Look for two trials in which all but one concentration stays constant.
In Trials 1 and 2, [A] remains constant, but [B] changes.
In Trials 2 and 4, [B] remains constant, but [A] changes.
So the rate law is