What is liquefaction of gases?

Short Answer

Liquefaction of gases is the process of converting a gas into a liquid by applying pressure, lowering temperature, or using both methods together. When gases are cooled, their particles lose energy and move closer, making it easier for them to change into liquid form.

This process is widely used in industries to store gases like oxygen, nitrogen, carbon dioxide, and LPG in cylinders or tanks. Liquefaction makes gases easier to transport, store, and use in various applications.

Detailed Explanation :

Liquefaction of Gases

Liquefaction of gases refers to the process in which a gas is transformed into a liquid by changing its pressure and temperature. Under normal conditions, gases have particles that are spread far apart and move freely with high kinetic energy. This prevents them from coming close enough to form a liquid. To convert a gas into a liquid, we must bring its particles close together and reduce their movement.

This can be done in two main ways:

  • Lowering the temperature to reduce the kinetic energy of particles
  • Increasing the pressure to force particles closer

Often, both methods are used together for efficient and complete liquefaction.

This process is extremely important in industrial applications where gases need to be stored or transported in liquid form because liquids take up much less space than gases.

How Liquefaction of Gases Works

The process of liquefying gases depends on the principles of kinetic theory. Gas particles move randomly at high speeds. Their movement depends on temperature and pressure. To convert a gas into a liquid:

  • The particles must be slowed down
  • The distance between them must be reduced
  • Intermolecular forces must become strong enough to hold them together
  1. Cooling

When a gas is cooled, its particles lose kinetic energy. They start moving more slowly and come closer together. As the temperature continues to drop, the gas reaches a point where its molecules are close enough to form a liquid. This is known as condensation.

  1. Applying Pressure

Pressure forces gas particles closer. If enough pressure is applied, intermolecular forces become strong enough to turn the gas into a liquid.

For many gases, pressure alone can liquefy them—but only if the temperature is below the critical temperature. Above the critical temperature, pressure alone cannot liquefy a gas.

  1. Combination of Cooling and Pressure

In most cases, both cooling and pressure are used together. This makes liquefaction faster and more efficient. For example:

  • Oxygen and nitrogen used in hospitals
  • LPG in cooking cylinders
  • Carbon dioxide in fire extinguishers

All of these are produced through combined cooling and compression.

Critical Temperature and Its Role in Liquefaction

Critical temperature is the highest temperature at which a gas can be converted into a liquid by applying pressure.

  • Below the critical temperature → gases can be liquefied easily
  • At or above critical temperature → cooling is necessary

For example:

  • Carbon dioxide has a critical temperature of 31°C
  • This means CO₂ must be cooled below 31°C before pressure can liquefy it

Understanding critical temperature is essential for liquefaction.

Examples of Liquefaction in Daily Life

  1. LPG Cylinders

Liquefied Petroleum Gas (LPG) is stored in cylinders by applying high pressure. This turns propane and butane into liquid form.

  1. LNG Tanks

Liquefied Natural Gas (LNG), mainly methane, is cooled to very low temperatures to convert it into a liquid. This reduces its volume 600 times, making transportation easy.

  1. Oxygen Cylinders

Oxygen used in hospitals is stored as a liquid because liquid oxygen takes up less space.

  1. Carbon Dioxide in Fire Extinguishers

CO₂ is kept liquefied under pressure and released as gas when needed to put out fires.

  1. Aerosol Cans

Perfumes, deodorants, and insect sprays use liquefied gases for smooth spraying.

Methods Used in Industries for Liquefaction

Industries use the following techniques:

  1. Joule–Thomson Effect

When gases expand suddenly, they cool down. This cooling helps in liquefaction.

  1. Linde’s Process

A gas is compressed, cooled, expanded, and repeatedly cycled until it finally becomes liquid.

  1. Claude’s Process

Uses both isentropic expansion and external cooling to liquefy gases like oxygen and nitrogen.

These scientific methods help liquefy even difficult gases like hydrogen and helium.

Uses of Liquefied Gases

Liquefied gases have many applications:

  • Medical oxygen for patients
  • LPG for cooking
  • Liquid nitrogen for freezing
  • Liquid hydrogen for rockets
  • CO₂ for carbonated drinks
  • Liquid ammonia for fertilizers

These uses show how important the liquefaction process is in industry, medicine, and daily life.

Importance of Liquefaction of Gases

Liquefaction makes gases:

  • Easier to transport
  • Safer to store
  • Cheaper to use
  • More efficient in industrial processes

Liquefaction is essential in refrigeration, air conditioning, fuel technology, food preservation, and scientific research.

Conclusion

Liquefaction of gases is the process of converting a gas into a liquid by cooling, applying pressure, or using both methods. It depends on reducing the kinetic energy of gas particles and bringing them closer. Critical temperature and pressure play a key role in deciding how easily a gas can be liquefied. Liquefied gases are widely used in everyday life, industries, and medical fields, making this process extremely important in modern science and technology.