Question

About \(20 \mathrm{~km}\) above the earth, is the ozone layer. Which one of the following statements about ozone and ozone layer is true? (a) conversion of \(\mathrm{O}_{3}\) to \(\mathrm{O}_{2}\) is an endothermic reaction (b) it is beneficial to us as it stops ultraviolet radiation (c) ozone has a triatomic linear molecule (d) it is harmful as it stops useful radiations

Short answer

The true statement is (b): the ozone layer is beneficial as it stops ultraviolet radiation.

Step-by-step solution

Understand the Options

The problem provides four statements about the ozone layer. We need to determine which one is true. Each statement offers different characteristics or impacts of the ozone layer or ozone itself.

Analyze Option (a)

Option (a) argues that the conversion of \( \mathrm{O}_{3} \) to \( \mathrm{O}_{2} \) is an endothermic reaction. This conversion is typically exothermic, releasing energy as ozone breaks down into oxygen molecules. Thus, this statement is false.

Evaluate Option (b)

Option (b) claims that the ozone layer is beneficial because it stops ultraviolet (UV) radiation. This is true, as the ozone layer absorbs a significant portion of the sun's harmful UV radiation, protecting organisms on Earth from potential damage.

Review Option (c)

Option (c) states that ozone has a triatomic linear molecule. While ozone is indeed composed of three oxygen atoms, its molecular shape is bent, not linear, due to the distribution of electrons. Therefore, this statement is false.

Check Option (d)

Option (d) suggests that the ozone layer is harmful because it stops useful radiations. This is misleading since the primary concern of the ozone layer is blocking harmful UV radiation, not useful radiation. Thus, this statement is false.

Key concepts

UV Radiation

The ozone layer plays a crucial role in protecting life on Earth from harmful solar emissions. A significant portion of this protection comes from its ability to block and absorb ultraviolet (UV) radiation. UV radiation is a type of energy emitted by the sun, which falls into three categories: UV-A, UV-B, and UV-C.
* **UV-A:** This is the least harmful form of UV radiation. However, it penetrates deep into the skin layers, contributing to long-term skin issues such as aging and certain skin cancers.
* **UV-B:** The ozone layer effectively absorbs the majority of UV-B rays, which are responsible for sunburn and have been linked to more severe skin cancers, such as melanoma.
* **UV-C:** The most dangerous, though it is entirely absorbed by the ozone and atmospheric oxygen and thus does not reach the Earth's surface.
By effectively filtering these harmful rays, the ozone layer helps in preventing DNA damage in living organisms. Without this protective barrier, life on Earth would be significantly more vulnerable to the adverse effects of UV radiation.

Ozone Decomposition

Ozone (\( \text{O}_3 \)) is continually formed and broken down in the stratosphere. This process is crucial in maintaining the balance of the ozone layer. Ozone decomposition primarily refers to its conversion back into oxygen molecules (\( \text{O}_2 \)), which occurs in an exothermic reaction.
The breakdown of ozone into oxygen involves releasing energy as the bonds in ozone molecules are broken. This decomposition is crucial because it helps to absorb UV radiation in the process, thereby reducing its intensity.
Further, human activities can accelerate ozone decomposition through the release of certain chemicals, such as chlorofluorocarbons (CFCs). These substances break down in the stratosphere, releasing chlorine atoms that catalytically break ozone apart, leading to ozone depletion.
Managing this balance is essential for ensuring the continued protective function of the ozone layer, shielding us from excessive UV radiation.

Molecular Geometry of Ozone

Understanding the structure of ozone helps explain why it is so effective at absorbing UV radiation. Ozone is a molecule composed of three oxygen atoms. But, unlike a linear structure, it has a bent shape, resulting from its electron distribution and hybridization.
* **Bent Structure:** The molecular geometry of ozone is angular or bent, with a bond angle of approximately 116.8 degrees. This shape is due to the way electrons are arranged around the central oxygen atom, leading to repulsion that causes the molecule to adopt its distinct shape.
* **Resonance Structures:** Ozone is also characterized by resonance, meaning its double bond can shift locations between the oxygen atoms. This contributes to its stability and reactivity as it can absorb a wide spectrum of UV light.
By understanding these structural aspects, we gain insight into why ozone can efficiently absorb UV radiation, playing a vital role in protecting life on Earth from harmful solar emissions.