Question

\(\mathrm{CFCl}_{3}\) is responsible for the decomposition of ozone into oxygen. Which of the following reacts with ozone to form oxygen? (a) \(\mathrm{Cl}_{2}\) (b) \(\mathrm{Cl}^{-}\) (c) \(\mathrm{F}^{-}\) (d) \(\mathrm{Cl}^{*}\)

Short answer

(d) \(\mathrm{Cl}^{*}\)

Step-by-step solution

Understanding the Problem

We need to identify the species that reacts with ozone to form oxygen. We are given four options, and the correct one will be involved in the mechanism for ozone decomposition initiated by CFCl extsubscript{3}.

Identifying the Mechanism

The mechanism by which CFCl extsubscript{3} leads to ozone decomposition involves the release of chlorine radicals (Cl extsuperscript{*}). Chlorine radicals are known to react with ozone (O extsubscript{3}) to form oxygen.

Analyzing the Options

For ozone decomposition, chlorine radicals (Cl extsuperscript{*}) are the active species. These radicals attack ozone molecules, leading to the formation of O extsubscript{2}. Among the given options, only (d) Cl extsuperscript{*} represents a chlorine radical.

Conclusion

Chlorine radicals (Cl extsuperscript{*}) are responsible for reacting with ozone and converting it into oxygen. Thus, the correct answer is (d) \(\mathrm{Cl}^{*}\).

Key concepts

CFCl3

Chlorofluorocarbons (CFCs) like \(\mathrm{CFCl}_3\), also known as trichlorofluoromethane, play a significant role in atmospheric chemistry. These compounds were widely used in products such as refrigerants and aerosol propellants until it was discovered that they contribute to ozone layer depletion. CFCl3 is stable in the lower atmosphere, but when it reaches the stratosphere, it is broken down by ultraviolet (UV) radiation.
Upon decomposition by UV light, CFCl3 releases chlorine atoms which are introduced into the stratosphere. These free chlorine atoms, or radicals, are highly reactive and become a part of the catalytic cycle responsible for the breakdown of ozone.
Importantly, one single molecule of CFCl3 can release multiple chlorine atoms, which means a single CFC molecule has the potential to destroy several ozone molecules once UV radiation triggers its decomposition.

Chlorine Radicals

Chlorine radicals, represented chemically as \(\mathrm{Cl}^{*}\), are incredibly reactive species due to the presence of an unpaired electron. This reactivity makes them crucial players in the destruction of ozone molecules in the stratosphere. When CFCl3 and similar compounds are broken down by UV light, chlorine radicals are released and initiate a destructive cycle called the ozone depletion cycle.
These radicals react with ozone (\(\mathrm{O}_3\)) in the following manner:
\(\mathrm{Cl}^{*} + \mathrm{O}_3 \rightarrow \mathrm{ClO} + \mathrm{O}_2\)
This reaction produces chlorine monoxide (ClO) and oxygen molecules. The chlorine monoxide can further react with atomic oxygen to release the chlorine radical back into the cycle, continuing the process of ozone destruction:
\(\mathrm{ClO} + \mathrm{O} \rightarrow \mathrm{Cl}^{*} + \mathrm{O}_2\)
It's critical to understand that a single chlorine radical can destroy thousands of ozone molecules before it is eventually neutralized.

Ozone

Ozone, with the chemical formula \(\mathrm{O}_3\), is a molecule composed of three oxygen atoms. It is primarily found in the Earth's stratosphere and forms the ozone layer, which plays a crucial role in protecting life on Earth by absorbing the majority of the sun's harmful ultraviolet (UV) radiation.
The presence of ozone in the stratosphere is a delicate balance between its formation and destruction. Ozone is naturally formed when UV light splits an oxygen molecule (\(\mathrm{O}_2\)) into two separate oxygen atoms, and one of those atoms combines with another \(\mathrm{O}_2\) molecule.
However, human-made compounds like CFCl3 disrupt this balance by introducing chlorine radicals into the atmosphere, accelerating the breakdown of ozone into oxygen molecules (\(\mathrm{O}_2\)).
This reduced ozone concentration leads to the thinning of the ozone layer, allowing more UV radiation to reach the Earth's surface, which can result in environmental and health issues such as increased skin cancers and cataracts.