Which statement(s) is/are applicable above critical temperature?
- A gas cannot be liquified
- The surface tension of a liquid is very high
- A liq. phase cannot be distinguished from a gas phase.
- Density changes continuously with P or V.
The Correct Option is A, C, D
Solution and Explanation
Critical Temperature Concept:
The critical temperature ($T_c$) of a substance is the highest temperature at which it can exist as a liquid, regardless of the pressure applied. Above this temperature, the kinetic energy of the molecules is too high for intermolecular attractions to bring them together into a liquid phase.
Key implications above $T_c$:
- (A) A gas cannot be liquified:
This is true. Above the critical temperature, even applying high pressure cannot condense the gas into a liquid. - (C) A liquid phase cannot be distinguished from a gas phase:
This is true. At and above the critical point, the properties of gas and liquid merge into a single supercritical fluid, with no clear boundary between phases. - (D) Density changes continuously with $P$ or $V$:
This is true. In a supercritical fluid (beyond $T_c$), the substance shows continuous and smooth changes in density with pressure or volume, rather than abrupt phase transitions.
Correct options: (A), (C), and (D)
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Concepts Used:
Behaviour of Real Gases
Real gases are gases that do not follow the ideal gas law, which assumes that gas particles have negligible volume and no intermolecular forces. In reality, gas particles do have volume and interact with each other, leading to deviations from ideal gas behavior.
The behavior of real gases can be described using various gas laws, such as the van der Waals equation and the virial equation. These equations take into account the effects of gas particle size and intermolecular forces on gas behavior.
One important property of real gases is compressibility. Real gases are more compressible than ideal gases, meaning that they can be compressed to a smaller volume at the same pressure. This is due to the fact that gas particles occupy a finite amount of space and are subject to intermolecular forces that can cause them to come closer together.
Also Read: Derivation from Ideal Gas Behavior
Another property of real gases is that their behavior is strongly affected by temperature and pressure. At high pressures and low temperatures, real gases tend to deviate more from ideal gas behavior. This is because the intermolecular forces become stronger and the gas particles are closer together.
Real gases also exhibit a phenomenon called condensation, where gas particles condense into a liquid or solid state when cooled or compressed sufficiently. This is due to the fact that the intermolecular forces become strong enough to overcome the kinetic energy of the gas particles, causing them to condense into a denser state.
Overall, the behavior of real gases is complex and influenced by various factors such as temperature, pressure, and intermolecular forces. Understanding the behavior of real gases is important in many scientific and industrial applications, such as in chemical reactions, power generation, and refrigeration.