Problem 13 - A Complete Resource Book in Chemistry for JEE Main

Question

The temperature below which a gas can be made to liquefy by variation in pressure is called its (a) inversion temperature (b) critical temperature (c) neutral temperature (d) curie point

Step-by-Step Solution

Answer

(b) critical temperature

Step 1: Understanding Inversion Temperature

The inversion temperature is not directly related to the liquefaction of gases by pressure. It is the temperature at which the Joule-Thomson effect changes sign. It is not concerned with converting gases to liquids by pressure.

Step 2: Exploring Critical Temperature

The critical temperature is the temperature above which a gas cannot be liquefied by applying any amount of pressure. Below this temperature, it is possible to liquefy the gas by pressure changes, which makes it the correct answer related to liquefaction.

Step 3: Defining Neutral Temperature

Neutral temperature has more context in thermodynamics and temperature measurement but is not commonly used in reference to the liquefaction of gases.

Step 4: Curie Point Explained

The Curie point is the temperature at which a ferromagnetic material loses its permanent magnetism or ferroelectricity. It is unrelated to the concept of gas liquefaction.

Key Concepts

Liquefaction of Gases

Liquefaction refers to the process of turning a gas into a liquid. This is a critical concept in chemistry and physics, especially in industries where gases need to be stored or transported. The ability to liquefy a gas depends on its critical temperature, which is the highest temperature at which a gas can become a liquid under any pressure. If the temperature of the gas is above this level, it remains in the gaseous state. Liquefaction is usually achieved by compressing the gas, which involves raising the pressure and lowering the temperature to below the critical temperature.
Understanding the critical temperature is essential as it determines the conditions required to turn gaseous elements into liquids. For instance, carbon dioxide has a critical temperature of about 31°C, whereas for oxygen, it is -118.6°C. Knowing these temperatures helps in designing equipment like compressors and cooling systems for large-scale gas handling.
Key factors affecting liquefaction include:

• Temperature: It must be below the critical temperature for liquefaction to occur.
• Pressure: Higher pressure aids the liquefaction process.
• Gas Type: Different gases have different critical temperatures and pressures.

These factors are crucial when handling gases for industrial applications.

Joule-Thomson Effect

The Joule-Thomson effect is a fascinating phenomenon that occurs when a gas expands without exchanging heat with its surroundings. This effect is key in understanding how temperature changes as gases are either compressed or expanded. In simpler terms, the Joule-Thomson effect explains why gases may cool or heat when allowed to expand.
This cooling or heating depends on the initial temperature and pressure of the gas. For most gases, temperature decreases during expansion if they are below their inversion temperature. However, if they are above this point, expansion will increase the temperature. The inversion temperature is unique to each gas and is essential in practical applications like refrigeration and air conditioning, where controlled temperature changes are necessary.
The Joule-Thomson effect also relates indirectly to the liquefaction of gases. When gas is allowed to expand and cool below its critical temperature, it can help in further liquefying the gas by creating conducive temperature conditions.

Gas Pressure Variation

Understanding how gas pressure varies is crucial in controlling and predicting changes in a gas's state. When pressure on a gas is changed, it affects its volume and temperature too, based on the principles outlined in the ideal gas law. In the context of liquefaction, altering pressure is a primary technique used to transform gases into liquids.
By increasing pressure while keeping the temperature below the critical point, gases can be compressed into a lesser volume, encouraging the molecules to condense into a liquid. This principle forms the basis for many industrial and scientific processes. The reverse is also true; reducing pressure can cause a liquid to revert to its gaseous state if other conditions allow.
Gas pressure variation involves the following key principles:

• Boyle’s Law: At constant temperature, the volume of a gas is inversely proportional to its pressure.
• Charles’ Law: At constant pressure, the volume of a gas is directly proportional to its temperature.
• Combined Gas Law: Integrates Boyle’s and Charles’ laws to describe behaviors when both conditions change.

These principles are vital in maintaining system designs in manufacturing, storage, and transportation of gases, ensuring safety and efficiency.