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)  ext{Cl}^{*} reacts with ozone to form oxygen.

Step-by-step solution

Identify the Problem

We need to determine which compound reacts with ozone to form oxygen. The options provided are potential reactants in this process.

Recall the Ozone Depletion Reaction

In the stratosphere, chlorofluorocarbons like CFCs can release chlorine radicals. These chlorine radicals ( ext{Cl}^{*}) react with ozone ( ext{O}_3) to form oxygen ( ext{O}_2). The key species here is the chlorine radical, which is known to partake in catalytic cycles destroying ozone.

Analyze Each Option

-  ext{Cl}_2 does not participate in the conversion of ozone to oxygen. -  ext{Cl}^{-} is an ion, and ions do not play a role in these radical reactions. -  ext{F}^{-} is a fluoride ion, irrelevant to ozone chemistry via free radical reactions. -  ext{Cl}^{*} is a chlorine radical, which is directly involved in ozone decomposition to oxygen.

Select the Correct Answer

The correct answer is  ext{Cl}^{*}, as it is the species that reacts with ozone to convert it to oxygen through the catalytic cycle of ozone decomposition.

Key concepts

Chlorofluorocarbons

Chlorofluorocarbons, commonly known as CFCs, are compounds that contain chlorine, fluorine, and carbon. Developed in the early 20th century, they were once widely used as refrigerants, propellants in aerosol applications, and solvents. CFCs are stable compounds and are not reactive in the lower atmosphere, which initially seemed beneficial due to their non-toxic and non-flammable characteristics. However, this very stability causes them to accumulate in the atmosphere and gradually make their way to the stratosphere.
CFCs are particularly notorious for their role in stratospheric ozone depletion. When they reach the higher layers of the atmosphere, they are broken down by ultraviolet radiation. This process releases chlorine atoms into the stratosphere. One CFC molecule can release multiple chlorine radicals, which then act as catalysts in the breakdown of ozone into oxygen. These reactions are cyclical, meaning one molecule of chlorine can repeatedly destroy ozone molecules.
While once hailed as a technological innovation, the widespread use of CFCs has led to significant environmental concerns. Their ozone-depleting capabilities have resulted in regulatory measures worldwide, such as the Montreal Protocol, aiming to phase out their use.

Chlorine Radical

Chlorine radicals, denoted as \( \mathrm{Cl}^{*} \), are highly reactive species formed primarily from the photodissociation of chlorofluorocarbons in the stratosphere. A radical is a molecule that has an unpaired electron, making it extremely reactive. The main concern with chlorine radicals is their crucial role in depleting the ozone layer.
Once formed, chlorine radicals react with ozone \(( \mathrm{O}_3 )\) in a destructive catalytic cycle. This cycle typically involves two main steps:

• The chlorine radical combines with ozone to form chlorine monoxide \(( \mathrm{ClO} )\) and molecular oxygen \(( \mathrm{O}_2 )\).
• The \( \mathrm{ClO} \) then reacts with a free oxygen atom, regenerating the chlorine radical and producing another molecule of \( \mathrm{O}_2 \).

This cyclical nature means that a single chlorine radical can destroy thousands of ozone molecules before being removed from the cycle.
The concept of radicals in atmospheric chemistry highlights the extreme efficiency and danger posed by very small quantities of reactive species in affecting large-scale transformations.

Stratospheric Chemistry

Stratospheric chemistry is the study of chemical processes that occur in the stratosphere, a layer of the Earth's atmosphere that extends from about 10 to 50 kilometers above the Earth's surface. This region is crucial for life on Earth as it contains the ozone layer, which filters out harmful ultraviolet radiation from the sun.
Ozone in the stratosphere is primarily formed and maintained by interactions between solar radiation and oxygen molecules. However, human activities have introduced substances such as CFCs that disrupt this balance. Stratospheric chemistry has an intrinsic focus on reactions like the catalytic cycles that lead to ozone depletion.
A profound understanding of these chemical interactions is necessary for environmental protection and policy-making. Scientists use stratospheric chemistry to model how molecules like CFCs and other ozone-depleting substances behave over time and impact global climate change. By studying these processes, researchers can predict future trends and the potential for recovery of the ozone layer.
As environmental awareness grows, understanding stratospheric chemistry helps in devising strategies for reducing human impact on atmospheric chemistry, like reducing emissions of ozone-depleting substances and mitigating climate change implications.