The reaction NO(g) + O3(g) → NO2(g) + O2(g) is first order in each reactant with an activation energ — Kinetics Chemistry Question
Problem Context
The reaction NO(g) + O3(g) → NO2(g) + O2(g) is first order in each reactant with an activation energy, Ea, of 11.7 kJ/mol and a rate constant of k = 1.2 × 1010 .L mol–1 s–1 at 25 ˚C.
Calculate the value of the pre-exponential factor, A, in the equation k = Ae– Ea/RT.
Would the A factor for the chemical reaction NO(g) + N2O(g) → NO2(g) + N2(g) be expected to be larger or smaller than the A factor in the above reaction if each reaction occurs in a single step? Outline your reasoning.
Model Answer
The A factor for NO and N2O would be smaller than that for NO and O3 because there are fewer geometric arrangements involving NO and N2O molecules that could lead to a successful reaction. The probability of successful reactions are lower for NO and N2O.
Calculate the rate constant for this reaction at 75 ˚C.
The following two-step mechanism has been proposed for this reaction:
O3(g) → O2(g) + O(g) Step 1
NO(g) + O(g) → NO2(g) Step 2
State and explain whether this mechanism is consistent with the observed rate law.
Model Answer
This mechanism would give either Rate = k[O3] if first step is the slow one or if second step is slow. Since neither of these is Rate = k[NO][O3] this can’t be the mechanism.