Problem 69 - A Complete Resource Book in Chemistry for JEE Main

Question

About \(20 \mathrm{~km}\) above the earth there is an ozone layer. Which of the following statements about ozone and ozone layer are false? (1) The conversion of ozone to oxygen is an endothermic reaction. (2) Ozone layer is beneficial to us because ozone cuts out the ultraviolet radiation of the sun. (3) Ozone layer is harmful to us because it cuts off radiations useful for photosynthesis. (4) Ozone has a triatomic linear molecule. (a) 1,2 and 3 (b) 1,3 and 4 (c) 2,3 and 4 (d) 3 and 4 only

Step-by-Step Solution

Answer

The false statements are 1, 3, and 4 (b).

Step 1: Evaluate Statement 1

Statement 1 states that the conversion of ozone to oxygen is an endothermic reaction. This is incorrect because the conversion of ozone (\(O_3\)) to oxygen (\(O_2\)) is actually an exothermic reaction, meaning it releases energy.

Step 2: Evaluate Statement 2

Statement 2 claims that the ozone layer is beneficial because it cuts out ultraviolet radiation from the sun. This statement is correct as the ozone layer absorbs a significant portion of the sun's harmful ultraviolet radiation, protecting life on Earth.

Step 3: Evaluate Statement 3

This statement posits that the ozone layer is harmful because it blocks radiations useful for photosynthesis. This is false because photosynthesis primarily relies on visible light, not the ultraviolet radiation that the ozone layer blocks. Thus, the ozone layer does not impede photosynthesis.

Step 4: Evaluate Statement 4

This statement claims that ozone has a triatomic linear molecule. This is false because ozone's molecular structure is bent, not linear, even though it is composed of three oxygen atoms.

Step 5: Determine the False Statements Combination

Based on the analysis: Statement 1 is false, as is Statement 3 and Statement 4. Therefore, the false statements are 1, 3, and 4.

Key Concepts

Exothermic Reaction

In chemistry, the term "exothermic reaction" refers to a process where energy, often in the form of heat, is released into the surrounding environment. An example of this is when ozone \((O_3)\) converts to oxygen \((O_2)\). During this transition, energy in the form of heat is emitted, making it an exothermic process.

To better understand this, think of an exothermic reaction as a system releasing energy. As these reactions release heat, they often cause a temperature increase in their immediate surroundings. This is the opposite of endothermic reactions, where energy is absorbed, usually causing a surrounding temperature drop.

Exothermic reactions are crucial in many natural processes and industrial applications. They are key in combustion reactions, which provide energy for heating, electricity, and propulsion systems.

Ultraviolet Radiation

Ultraviolet (UV) radiation is a type of electromagnetic radiation that comes from the sun and is invisible to the human eye. It has shorter wavelengths than visible light, meaning it has more energy. While UV radiation is mostly known for its harmful effects, such as skin damage and increased cancer risk, it plays an essential role in our environment.

The ozone layer, located about 20 kilometers above Earth, serves a crucial protective function by absorbing a large percentage of incoming ultraviolet radiation from the sun. This absorption prevents most UV radiation from reaching the Earth's surface, thereby reducing its harmful impacts.

One might wonder about the relationship between photosynthesis and UV radiation. The concern is unfounded because photosynthesis primarily uses visible light, not UV radiation. Thus, the ozone layer does not hinder the processes plants need for growth.

Molecular Structure

Molecular structure describes the arrangement of atoms within a molecule. Understanding this structure is vital in determining the molecule's properties and behavior. A well-known example is ozone, which plays a significant role in protecting life on Earth.

Ozone \((O_3)\) is composed of three oxygen atoms. Contrary to some misunderstandings, it does not have a linear structure. Instead, the molecule is bent or V-shaped. This is due to the specific electronic arrangement that causes the molecule to form angles rather than a straight line.

The bent shape of ozone is essential for its functionality in absorbing UV radiation. The specific angle and distribution of electrons allow ozone to effectively capture and reduce the harmful effects of solar radiation, highlighting the importance of understanding molecular structures.