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

The correct answer is (b) critical temperature.

Step 1: Understanding the Problem

We need to identify the term used for the temperature below which a gas can be made to liquefy just by varying pressure. This term is associated with the physical properties of gases and their phase transitions.

Step 2: Identifying Key Terms

Inversion temperature is when the Joule-Thomson coefficient changes sign. The critical temperature is the highest temperature at which a gas can be liquefied by pressure alone. Neutral temperature is not relevant here, and the Curie point is the temperature at which certain materials lose permanent magnetism.

Step 3: Analyzing Each Option

(a) Inversion temperature is related to inversion points in thermodynamics, not liquefaction. (b) Critical temperature is the correct term for the highest temperature at which a gas can still be liquefied by just compressing it. (c) Neutral temperature is not relevant to gas liquefaction. (d) Curie point relates to magnetism, not gas liquefaction.

Step 4: Conclusion

Based on the definitions, the critical temperature (option b) is the correct choice. It is the temperature above which a gas cannot be liquefied by pressure alone.

Key Concepts

Gas Liquefaction

Gas liquefaction is a fascinating process where a gas is converted into a liquid by cooling or compressing it. This is crucial for practical applications, such as storing gases or using them as fuels or coolants. To understand this process, think about air being turned into liquid oxygen or liquid nitrogen, which are then used in hospitals and industrial settings. Liquefying gas involves bringing it to a temperature below its critical temperature where the pressure can effectively turn it into liquid. When a gas is compressed, its molecules are pushed closer together. If the temperature is also reduced, the interactions between the molecules become strong enough to hold them in a liquid state:

• Critical Temperature: The highest temperature at which gas can be liquefied by pressure alone.
• Pressure: Applying pressure reduces the volume and increases the density.
• Cooling: Reducing temperature helps molecular bonds form a liquid.

Successfully achieving liquefaction depends on knowing the critical temperature. The gas won't liquefy above this threshold, no matter the pressure applied.

Phase Transitions

Phase transitions describe the transformation from one state of matter to another, like from solid to liquid, or liquid to gas. In the case of gas liquefaction, the transition is from gas (vapor) to liquid. This transition happens through changes in temperature and pressure. At a particle level,

• Particles in a gas move freely and randomly.
• Lower temperature slows particles down, reducing energy and allowing them to come closer.
• Pressure forces particles closer together, increasing interaction potential.

Understanding phase transitions is key for gas liquefaction. The timing of cooling or compressing must be appropriate to achieve a successful transition. A miscalculation or incorrect understanding of the conditions can prevent the phase change from occurring. Phase transitions leverage physical property changes to optimize gas states for practical use and storage.

Physical Properties of Gases

The behavior and characteristics of gases are governed by their physical properties. These properties are essential to understanding how gases transition between phases. In gas liquefaction, the following properties play critical roles:

• Temperature: Influences kinetic energy and molecular motion.
• Pressure: Affects volume and density, pivotal in liquefaction efforts.
• Volume: Changes as pressure and temperature fluctuate.

To transition a gas to a liquid efficiently, these properties must be controlled carefully. For example, above the critical temperature, no amount of pressure will liquefy a gas. Knowing these properties informs processes to store gases, transport them, and utilize them in industry or science. Understanding the physical properties of gases allows for breakthroughs in technology and applications, notably in refrigeration, energy production, and transportation sectors.