For the reaction
`2H_2(g)+2NO(g)rarrN_2(g)+2H_2O(g)`
the proposed mechanism is as followed
(i) `2NO(g) (ii)`N_2O_2(g)+H_2(g)rarrN_2O(g)+H_2O(g)`
`N_2O(g)+H_2(g)rarrN_2(g)+H_ 2O(g)`
If the second step is the rate determining step then what Is the molecularity of the reaction

Explanation

(a) Molecularity is the number of atoms, molecules or ions of the reacting species undergoing simultaneous collision in each elementary step.
Therefore, molecularity of step (1)=2 Molecularity of step (11)=2. Molecularity of step (iii) = 2 gives by the following expression.
Rate = `k [N_2O_2] [H_2]`
From step (i)
Equilibrium constant, `K= ([N_2O_2])/([NO]^2)`
`[N_2O_2]=K[NO]^2`
Substituting in (iv)Rate = `k.K [NO]^2 [H_2]`
`= k. [NO]^2 [H_2]` where `k. =k xx K`
`therefore` Overall order of the reaction=2+1=3
(c) The rate law expression is ,
Rate = `k.[NO]^2 [H_2]`