Problem 22 - A Complete Resource Book in Chemistry for JEE Main

Question

The extent of adsorption of a gas on a solid depends upon (a) nature of gas (b) temperature of gas (c) pressure of gas (d) all of these

Step-by-Step Solution

Answer

The extent of adsorption depends on all of these factors: nature of gas, temperature, and pressure.

Step 1: Identifying the Concept

Before we start solving the problem, we need to identify the concept it is related to. The question relates to adsorption, which is the process by which a gas accumulates on the surface of a solid.

Step 2: Understanding Factors Influencing Adsorption

We need to understand the factors that influence adsorption. Adsorption is influenced by the nature of the gas (how easily it interacts with the solid surface), temperature (lower temperatures typically result in greater adsorption for physical adsorption), and pressure (increased pressure can push more gas molecules onto the solid surface).

Step 3: Considering Each Option

Now let's consider each option one by one: - (a) Nature of gas: This affects how strongly the gas molecules adhere to the solid. - (b) Temperature of gas: Affects the kinetic energy of molecules; lower temperatures favor adsorption. - (c) Pressure of gas: In accordance with Le Chatelier's principle, higher pressure increases adsorption. Each factor does affect adsorption.

Step 4: Choosing the Correct Option

Since all the factors mentioned (nature of the gas, temperature, and pressure) affect the extent of adsorption, the correct answer is option (d) 'all of these.' Therefore, the extent of adsorption of a gas on a solid depends on the nature of the gas, temperature, and pressure.

Key Concepts

Nature of Gas

The nature of a gas plays a significant role in the adsorption process. Each gas has its unique properties that determine how it interacts with a solid surface. These properties include:

• Molecular weight: Heavier gases tend to be adsorbed more easily due to their higher Van der Waals forces.
• Polarity: Polar gases will generally be attracted more strongly to polar surfaces because of dipole-dipole interactions.
• Chemical affinity: Some gases have a natural affinity for specific solids that enhance adsorption strength.

The composition and characteristics of the gas determine how strongly or weakly it adsorbs onto a material. Understanding the nature of the gas gives insight into selecting the appropriate solid for optimal adsorption.

Temperature Effect on Adsorption

Temperature has a profound impact on the adsorption capacity of gases. For physical adsorption, where weak Van der Waals forces are at play, lower temperatures favor adsorption. Here’s why:

• At lower temperatures, the kinetic energy of gas molecules decreases.
• With less energy, the molecules move slower and have a better chance of settling on the surface.

However, in chemisorption, which involves stronger chemical bonds, a slight increase in temperature can sometimes increase adsorption by overcoming activation energy thresholds. It’s crucial to know the type of adsorption involved to predict temperature effects accurately.

Pressure Effect on Adsorption

Pressure influences the adsorption of a gas significantly. Higher pressure usually means more gas molecules are present and available to be adsorbed. Here's how:

• According to Le Chatelier's principle, increasing the pressure shifts the equilibrium towards the side of less volume, which in the case of gas-solid adsorption, is the solid surface.
• This results in more gas particles being forced onto the solid surface, enhancing adsorption.

For example, gas adsorption in carbon filters works more efficiently at higher pressures. Thus, understanding pressure's role helps in designing effective adsorption systems.