Critical temperature

Definition

The critical temperature is the temperature above which a gas cannot be liquefied, regardless of the pressure applied. It represents the highest temperature at which a substance can exist as a liquid.

5 Must Know Facts For Your Next Test

1. The critical temperature marks the end point of the phase boundary between liquid and gas states.
2. Above the critical temperature, distinct liquid and gas phases do not exist; instead, there is only one supercritical fluid phase.
3. For water, the critical temperature is approximately 374°C (647 K).
4. Critical temperatures are unique to each substance and depend on intermolecular forces; stronger forces generally result in higher critical temperatures.
5. In thermodynamics, knowledge of a substance's critical temperature is essential for understanding its phase behavior under various conditions.

Review Questions

• What happens to a gas when it is compressed above its critical temperature?
• How does intermolecular force affect a substance's critical temperature?
• Why can't a gas be liquefied above its critical temperature regardless of pressure?

Related terms

Phase Change:

A transition between different states of matter such as solid, liquid, and gas.

Supercritical Fluid:

A state of matter beyond the critical temperature where distinct liquid and gas phases do not exist.

Triple Point:

$$The specific combination of pressure and temperature at which all three phases (solid, liquid, and gas) coexist in equilibrium.$$