What is an example of a rate law practice problem?
Here's an example that uses the method of initial rates.
Determine the rate law for the reaction A + 2B →C + 2D.
Expt.·····[A]₀/mol·L⁻¹·····[B]₀/mol·L⁻¹·····Init. Rate /mol·L⁻¹min⁻¹
···1··············0.10···················0.10·······················3.0 x 10⁻⁴
···2·············0.30··················0.30·····················9.0 x 10⁻⁴
···3·············0.10···················0.30······················3.0 x 10⁻⁴
The rate law has the form
In experiments 1 and 3, we have doubled [B]₀ and kept [A]₀ constant.
Doubling [B]₀ did not change the rate, so the order is zero with respect to B (
In experiments 3 and 2, we have tripled [A]₀ and kept [B]₀ constant.
Tripling [A]₀ tripled the rate, so the reaction is first order with respect to A (
The rate law is
The video below gives another example of using the method of initial rates to determine a rate law.