question_answer

  The possible mechanism for the reaction \[2NO(g)+{{O}_{2}}(g)\xrightarrow{\,}\,2N{{O}_{2}}(g)\]is (i)  \[NO+{{O}_{2}}N{{O}_{3}}\,(\text{Fast})\] (ii) \[N{{O}_{3}}+NO\,N{{O}_{2}}+N{{O}_{2}}\,(\text{Slow})\] What is the predicted rate law and order of the reaction?

Answer:

                  The rate law is given by the slow step. \[\therefore \]  Rate \[={{k}_{1}}[]N{{O}_{3}}]\,[NO]\] The equilibrium constant (K) as predicted by the fast step is: \[K=\frac{[N{{O}_{3}}]}{[NO]\,[{{O}_{2}}]}\] or            \[[N{{O}_{3}}]\,=K[NO]\,[{{O}_{2}}]\] Substituting the value of [N03] in eqn. (i) Rate \[(\text{Here}\,k'={{k}_{1}}K')\] Order of reaction =2+1=3