Question

13.49. Write rate laws and determine the units of the rate constant (using the units M for concentration and s for time) for the following reactions: a. The reaction of oxygen atoms with NO, is first order in both reactants. b. The reaction between NO and Cl, is second order in NO and first order in Cl. c. The reaction between Cl2 and chloroform (CHC1z) is first order in CHCl3 and one-half order in C1. *d. The decomposition of ozone (O3) to O2 is second order in O3 and an order of -1 in O atoms.

Answer 1

Rate law: The rate of reaction is directly propotional to the reactant concentration,each concentration being raised to some power.

E.g: A undergoing reaction.

Rate= k [A]

Order of reaction:

The order of reaction is the sum of the power of concentration of concentration in the rate law.

E.g: rate= k[A]^m [B]ⁿ

order= (m+n)

a) The reaction of oxygen atom with NO₂ is first order in both reactant.

Ans: rate=k [NO₂]¹ [O]¹

^{overall order=1+1=2}

This is second order reaction so unit is mol^-1 lit s^-1

b)The reaction between NO and Cl₂ is second order in NO and first order in Cl₂

Ans: rate= k [NO]² [Cl₂]¹

^{overall order = 2+1 = 3}

This is third order reaction so unit is mol^-2 lit² s^-1

C) The reaction between Cl₂ and chloroform (CHCl₃) is first order in CHCl₃ and one-half order in Cl_2.

ans: rate = k[CHCl₃]¹ [Cl₂]^1/₂

overall order = 1+1/2 = 3/2

The order of this reaction is 3/2 and unit is mol^-1/₂ lit^1/2 s-1

d) The decomposition of ozone (O₃) to O₂ is second order in O₃ and an order of -1 in O atoms.

ans: ratr =[O₃]² [O]^-1

Overall order = 2 + (-1) = 1

This is first order reaction so unit is s^-1