Halons are fluorocarbons that contain bromine, such as CBrF3. They are used extensively as foaming agents for fighting fires. Like CFCs, halons are very unreactive and ultimately can diffuse into the stratosphere. (b) Propose a mechanism by which the presence of halons in the stratosphere could lead to the depletion of stratospheric ozone.

Verified step by step guidance

1. Identify the key components involved in the reaction: halons (e.g., CBrF3) and ozone (O3) in the stratosphere.
2. Understand that halons, like CFCs, can release bromine atoms when they are broken down by ultraviolet (UV) radiation in the stratosphere.
3. Describe how the bromine atoms (Br) released from halons can react with ozone (O3) to form bromine monoxide (BrO) and oxygen (O2).
4. Explain that bromine monoxide (BrO) can further react with atomic oxygen (O) to regenerate bromine atoms (Br) and produce more oxygen (O2), thus continuing the cycle.
5. Conclude that this catalytic cycle involving bromine atoms leads to the depletion of ozone because a single bromine atom can destroy many ozone molecules before being deactivated.

Key Concepts

Stratospheric Ozone Layer

The stratospheric ozone layer is a region of Earth's atmosphere that contains a high concentration of ozone (O3) molecules. It plays a crucial role in absorbing the majority of the sun's harmful ultraviolet (UV) radiation, protecting living organisms on Earth. The depletion of this layer can lead to increased UV exposure, resulting in adverse effects on human health and ecosystems.

Halons and Their Chemical Stability

Halons are a class of halogenated hydrocarbons that contain bromine and are known for their chemical stability and low reactivity. This stability allows them to persist in the atmosphere for long periods, enabling them to reach the stratosphere. Once there, halons can undergo photodissociation, releasing bromine atoms that are highly effective at catalyzing the breakdown of ozone molecules.

Ozone Depletion Mechanism

The mechanism of ozone depletion involves the release of reactive halogen species, such as bromine, which catalyze the destruction of ozone in the stratosphere. A single bromine atom can destroy thousands of ozone molecules through a series of reactions, leading to significant thinning of the ozone layer. This process is exacerbated by the presence of UV radiation, which initiates the breakdown of halons and releases the reactive halogen atoms.