In the stratosphere, the temperature-dependence of the rate constant for the con
ID: 547630 • Letter: I
Question
In the stratosphere, the temperature-dependence of the rate constant for the conversion of ozone to molecular oxygen by atomic chlorine (Cl (g) + O3 (g) ClO (g) + O2 (g)) follows the expression below: k =( 1.7 x 1010 Mt's! ) e-260K Note: M s and K are the units of the values they accompany. (a) Assume this reaction to be elementary and calculate the rate at 20 km where the concentra Cl and Os are 5 x 1017 M and 8 x 109 M, respectively, and the temperature is 220 K. (b) Calculate the standard enthalpy, entropy and Gibbs free energy of activation (AH, AS , :G) of the previous reaction at 220 K Interpret the value obtained for Suggest a possible structure for the transition state of this reaction and explain its main geometrical features. Taking into account the following standard enthalpies of formation, calculate the activation energy of the reverse reaction: CIO (g) + O2(g) Cl (g) + 03 (g) (c) AHr (kJ/mol) CIO 101.2 142.7 121.3 ClExplanation / Answer
a) rate = k[Cl][O3]
= (1.7 * 10^10) * e^(-260/220) * 5 * 10^-17 * 8 * 10^-9
= 2.085 * 10^-15 M/s
b) H0:
Subtract the sum of the heats of formation of the reactants from that of the products to determine delta H
H0 = (121.7 kJ/mol+ 142.7 kJ / mol) - (101 kJ/mol + 0)
= 163.4 kJ/mol
S0 :
S0 = [56.5+ 238.92] - [218.9 + 205]
= -128.48 J K-1 mol-1
G0= H0 - T S0
= 163.4 - 220 * -128.48
= `28429 J/mol
= 28.429 kJ/mol
The transition state in the reaction is ClO. Hypochlorite is an oxyacid of chlorine (HClO) containing monovalent chlorine that acts as an oxidizing or reducing agent.