Question

Critical temperature means above this temperature at any pressure, any gas can be (a) liquefied (b) not liquefied (c) both statements are correct (d) Solified

Short answer

The correct answer is (b) not liquefied.

Step-by-step solution

Understanding Critical Temperature

Critical temperature is the temperature beyond which a gas cannot be liquefied, no matter how much pressure is applied. In other words, above this temperature, gas particles have too much kinetic energy to be forced into a liquid state by pressure.

Evaluating the Statements

Looking at the given options, we can evaluate each with respect to the defined concept of critical temperature. (a) refers to gases being 'liquefied' - which is incorrect as gases can't be liquefied above the critical temperature. (b) states that gases cannot be 'liquefied' - which is correct. (c) says 'both statements are correct' which still contains the incorrect statement (a), making it incorrect. (d) says 'solidified' which is not related to the concept of critical temperature as it involves changing to a solid phase, not a liquid one.

Key concepts

Gas Liquefaction

Gas liquefaction is the process of cooling a gas to the point where it becomes a liquid. This occurs when the kinetic energy of the gas molecules is reduced, typically by lowering the temperature, so that the intermolecular forces can bring them closer together. When these forces are strong enough to hold the particles in a fixed volume, the gas transitions into a liquid state.
However, gas liquefaction is not always possible. For each gas, there is a specific temperature known as the critical temperature. Above this temperature, no amount of pressure can liquefy the gas, because the particles have too much energy.
Understanding the critical temperature is crucial for applications such as liquefied natural gas production, where maintaining certain temperature and pressure conditions is vital.

Kinetic Energy

Kinetic energy refers to the energy that a particle has due to its motion. In gases, molecules are in constant motion, moving rapidly in random directions. This motion is due to their kinetic energy, which is directly related to the temperature of the gas.
At higher temperatures, gas molecules have more kinetic energy, meaning they move faster. This increased motion makes it harder for pressure to bring the gas molecules close enough to stick together and form a liquid.

• If the temperature is below the critical temperature, enough pressure can slow down the molecules' motion enough to allow liquefaction.
• Above the critical temperature, the kinetic energy is too high, preventing the molecules from being compressed into a liquid regardless of the pressure applied.

Understanding kinetic energy provides insight into why gases behave differently under varying temperatures and pressures.

Phase Transition

A phase transition is the process through which a substance changes its state, such as from a gas to a liquid. Phase transitions occur when energy is either absorbed or released by the substance, leading to changes in temperature or pressure.
In the case of liquefying gases, the transition from gas to liquid happens when the temperature is decreased or pressure is increased enough to bring the gas molecules together.
The critical temperature marks the boundary for this phase transition in gases. Below this temperature, gases can exist as liquids if sufficient pressure is applied. However, above this temperature, the energy levels of the gas particles are too high to allow a compact liquid form, hence, no phase transition to liquid occurs. Understanding phase transitions is crucial for industrial processes where controlling the state of a substance is necessary for efficiency and safety.

Pressure Effects on Gases

Pressure plays a vital role in gas behaviors, particularly in their transition to liquid form. By increasing the pressure exerted on a gas, the space between its molecules can be reduced, causing them to come closer together.
When studying gases below their critical temperature, increasing pressure is generally an effective way to encourage their liquefaction, as it helps overcome the kinetic energy keeping the particles apart.
However, the effectiveness of pressure changes dramatically when the temperature exceeds the critical threshold. No matter how high the pressure, it can't force the gas particles into a liquid state when they possess too much kinetic energy.

• Below critical temperature, pressure can significantly impact liquefaction.
• Above critical temperature, pressure alone cannot induce liquefaction.

Understanding the role of pressure in gas behaviors is essential for many sectors, particularly those involving gas storage and transportation.