Question

The reaction 2NO + Br2 → 2NOBr 
takes places through the mechanism given below : 
NO + Br2 ⇔ NOBr2 (fast)  
NOBr2 + NO → 2NOBr (slow) 
The overall order of the reaction is_____.

Answer 1

Correct Answer: 3

Solution:

 1. Identify the rate-determining step: The slow step is the rate-determining step, as it dictates the overall rate of the reaction. The slow step is: NOBr2 + NO → 2NOBr 

2. Write the rate law based on the slow step: Rate = k[NOBr2][NO] 

3. Express the concentration of the intermediate (NOBr2) in terms of reactants: Since the first step is a fast equilibrium, we can write its equilibrium constant (K): K = [NOBr2] / ([NO][Br2]) [NOBr2] = K[NO][Br2] 

4. Substitute the expression for [NOBr2] into the rate law: Rate = k(K[NO][Br2])[NO] Rate = kK[NO]²[Br2] 

5. Determine the overall order of the reaction: The overall order is the sum of the exponents in the rate law. Order = 2 (for NO) + 1 (for Br2) = 3 Therefore, the overall order of the reaction is 3.