What Is Critical Pressure? Easy Explained Guide

What Is Critical Pressure? Easy Explained Guide
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What is Critical Pressure? The critical pressure of a material is the pressure that must be applied in order to liquefy that substance at its critical temperature.

Critical Pressure

The Critical Pressure of a material is the pressure equivalent to the critical point (or the critical state) of the substance. 

The critical point of a material may be described as the point on the temperature and pressure scale in which a liquid substance can coexist with its vapour. 

At temperatures above the critical point of a material, it cannot be liquified with the application of any amount of pressure. 

The Critical Pressure of a material may, therefore, be described as the pressure that must be applied to a substance in order to liquefy it at its critical temperature. 

The critical pressure of a material is commonly indicated by the sign ‘PC’.

The three most frequent states of matter, namely solid, liquid, and gas, are known to be separated by phase boundaries. 

These phase boundaries are defined by the two fundamental variables that impact the physical state of a material — temperature and pressure

Therefore, the modification of the temperature-pressure combinations may assist locate a phase boundary. 

For example, the triple point of a material is a point at which a substance may exist in all three forms (solid, liquid, and gaseous) (solid, liquid, and gaseous). 

The temperature and pressure levels at the triple points of various substances are varied. 

For example, the triple point of water corresponds to 0.01 degrees Celsius (or 273.16 Kelvin) and 4.58 mm of mercury.

What is Critical Pressure? Easy Explained

In a similar approach, by obtaining a comparable temperature-pressure combination, the phase boundary that divides the liquid and the vapour state of a material may be determined. 

This temperature-pressure combination is frequently referred to as the critical point of the material. 

The pressure equivalent to the critical point of a material is the Critical Pressure of that substance.

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Critical Pressures Of Some Common Substances

  1. The Critical Pressure of water equates to 217.7 atm or 22,060 kiloPascals.
  1. The Critical Pressure of ammonia (chemical formula: NH3) equates to 111.3 atm or 11,280 kiloPascals.
  1. The Critical Pressure of chlorine (symbol: Cl) equals 76 atm or 7,700 kiloPascals.
  1. The critical pressure of helium (symbol: He) equates to 2.24 atm or 227 kiloPascals.
  1. The  Critical Pressure of nitrogen equates to 33.5 atm or 3390 kiloPascals.

Critical Pressure (FAQs)

What Is The Critical Pressure Of A Fluid?

The critical pressure of a fluid may be described as the vapour pressure of the fluid at its critical temperature (beyond which point, separate gas and liquid phases do not exist) (above which point, distinct gas and liquid phases do not exist). 

What Is The Critical Point Of Water?

The critical point of water is known to occur at a temperature point of 647 Kelvin (which is equivalent to 374 degrees Celsius and 705 degrees Fahrenheit) and a Critical Pressure of 22.064 MPa (which is about equal to 218 atmospheres of pressure) (which is roughly equal to 218 atmospheres of pressure).

What Occurs At Temperatures Over The Critical Temperature?

At temperatures that are greater than the critical temperature of a material, the molecules of the substance are known to have too much kinetic energy for the intermolecular forces of attraction to bind them together in the liquid phase.

Thus, above the critical temperature, the material cannot be liquefied.


What Is the Difference Between Triple Point And A Critical Point?

The triple point of a material is the temperature and pressure at which it may exist in all three states.

A material is said to be at its critical point when the absolute temperature associated with it is equal to its critical temperature and the pressure applied to it is equal to its critical pressure.

  • November 19, 2022