Critical Temperature: Know its Definition, Importance & Uses (2024)

Critical Temperature

Critical temperature can be defined as the temperature at and above which a substance's vapour cannot be condensed, regardless of the amount of pressure used, is known as the critical temperature of the substance.

As can be seen, the graph is displayed with temperature on the X-axis and pressure on the Y-axis. As a result, the critical point's X-axis value can be used to determine the critical temperature. The pressure necessary to cause a substance to liquefy at its critical temperature is known as the critical pressure of the material and is the equivalent Y-axis value of the critical point.

Importance of Critical temperature in thermodynamics

An element's critical point is primarily determined by its critical temperature and critical pressure. A supercritical liquid is likely to be the next state of the material. At a temperature above the critical temperature, a substance cannot change from its solid state into its liquid state, no matter how much pressure is applied. The molecules have enough kinetic energy to overcome the intermolecular forces of attraction when the temperature is higher than the critical temperature. The critical pressure is the lowest pressure needed to change a gas into its liquid state. The critical point is the point at which pressure and temperature are just right for liquefaction.

It is important to remember that the ideas of critical point and boiling point are known to be distinct from one another. The critical point is reached by combining pressure and temperature, whereas the boiling point is the temperature at which the element can be transformed to vapour. This occurs when the element is simultaneously liquid and gaseous.

Critical Point, Critical Temperature and Pressure

Critical Temperature: The temperature above which a substance cannot exist as liquid, no matter how much pressure is applied. Every substance has a critical temperature.

Critical Pressure : The Pressure required to liquify a vapor at its critical temperature.

Critical Point : The end point of pressure -temperature curve that determines the condition at which the liquid and vapour can co-exist. At higher temperatures pressure alone is not enough for the gases to liquify. Critical point is the point where the phase boundaries between critical temperature and pressure vanish.

Triple Point : The temperature and pressure at which the three phases i.e. solid, liquid and gas of a substance co-exist at thermodynamic equilibrium.

Critical temperature for common substances

The critical temperatures of some common substances are listed below:

• The critical temperature of ammonia is 405.5 K
• The critical temperature of carbon dioxide is 304.19 K
• The critical temperature of nitrogen is 126.2 K
• The critical temperature of water is 647.09 K
• The critical temperature of helium is 5.19 K
• The critical temperature of chlorine is 416.9 K
• The critical temperature of lithium is 3220 K
• The critical temperature of gold is 7250 K

Applications in Industry & Research

These are the different applications of critical temperature:

• It is used to determine the purity of substances in pharmceuticals.
• They helps in understanding the strength of intermolecular forces of attraction in gases which determines the temperature to liquify a gas at a given pressure..
• It helps in determining the maximum temperature at which refrigerant can be condensed.
• It is used in polymerisation reactions that require high temperature and pressure.

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