Study Guides/Chemistry/Critical Temperature
Study Guide · Chemistry

What is Critical Temperature?

In Physical Chemistry (States of Matter), the concept of Critical Temperature (Tc) is fundamental to understanding how gases are liquefied.

Question (Click to Flip)

What is critical temperature?

Answer

Critical temperature is the maximum temperature at which a substance can exist as a liquid. Above this temperature, a gas cannot be liquefied regardless of how much pressure is applied.

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Key Facts

Definition: Temperature above which a gas cannot be liquefied by pressure alone.

Symbol: Tc.

CO₂ Critical Temp: 30.98 °C.

Importance: Determines how easily a gas can be stored as a liquid.

Definition

The Critical Temperature (Tc) of a gas is the temperature above which the gas cannot be liquefied, no matter how much pressure is applied.

Every gas has a specific critical temperature. If the gas is hotter than this temperature, its kinetic energy is so high that intermolecular forces cannot pull the molecules together into a liquid, even if you compress them infinitely.

Examples of Critical Temperatures

  • Carbon Dioxide (CO₂): Tc = 30.98 °C. You can liquefy CO₂ at room temperature (25°C) by applying pressure. But at 32°C, no amount of pressure will turn it into a liquid.
  • Water (H₂O): Tc = 374 °C.
  • Helium (He): Tc = -267.9 °C. It is very hard to liquefy because it must be cooled close to absolute zero first.

Related Terms

  • Critical Pressure (Pc): The minimum pressure required to liquefy a gas exactly AT its critical temperature.
  • Critical Volume (Vc): The volume occupied by one mole of a gas exactly at its critical temperature and critical pressure.

Questions and Answers

What is critical temperature?+

Critical temperature is the maximum temperature at which a substance can exist as a liquid. Above this temperature, a gas cannot be liquefied regardless of how much pressure is applied.

Can CO2 be liquefied at 35 degrees Celsius?+

No. The critical temperature of CO₂ is 30.98 °C. At 35 °C, it is above its critical temperature, so it cannot be liquefied by pressure.

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