Chapter 11, Problem 11.6PAE

At what points in the Chapman cycle do photochemical reactions take place?

Interpretation Introduction

Interpretation:

The steps in the Chapman Cycle in which photochemical reactions occur should be identified.

Concept introduction:

➢ Ozone is being created and destroyed in the stratosphere.

➢ The chapman cycle involves photochemical reactions.

Answer to Problem 11.6PAE

Solution:

In the first step of the cycle a photochemical reaction takes place, the molecule oxygen absorbs energy from UV rays to produce 2 free radicals.

In the third step an ozone molecule absorbs some UV rays to produce a free radical and an oxygen molecule.

Explanation of Solution

Ozone and oxygen are in constant interaction with ultraviolet rays in the stratosphere, this process is called the “Chapman” cycle.

In the first step an oxygen molecule in presence with UV light with a wavelength less than 242 nm will be broken into 2 free radicals:

${\text{O}}_{\text{2}}+\text{high energy UV }\to \text{ 2O}•$

In a second step a free radical reacts with oxygen to form an ozone molecule:

$\text{O}•{\text{+O}}_2\to {\text{O}}_3$

In a third step an ozone molecule is broken into an oxygen molecule and a free radical in presence with uv light with a wavelength higher than 242 nm and lower than 320 nm.

${\text{O}}_3+\text{lower energy UV}\to \text{O}•{\text{+O}}_2$

In a fourth step an oxygen free radical reacts with an ozone molecule to generate 2 oxygen molecules

$\text{O}•{\text{+O}}_3\to 2{\text{O}}_2$

In the first step of the cycle a photochemical reaction takes place, the molecule oxygen absorbs energy from UV rays to produce 2 free radicals.

In the third step an ozone molecule absorbs some UV rays to produce a free radical and an oxygen molecule.

Conclusion

The chapman cycle absorbs UV rays turning them into heat.