How to Liquefy Atmospheric Gas?

To successfully liquefy an atmospheric gas (like Oxygen, Nitrogen, or Carbon Dioxide), you must simultaneously do two things:

1. Increase the Pressure (Apply high pressure).
2. Decrease the Temperature (Cool the gas).

The state of matter (solid, liquid, or gas) depends entirely on the distance between its particles and their kinetic energy.

• Increasing Pressure: When you apply high pressure to a gas using a piston inside a cylinder, you force the widely scattered gas particles to come very close together.
• Decreasing Temperature: Even if particles are close together, if they are hot, they vibrate violently and push each other apart. By lowering the temperature, you remove their heat energy (kinetic energy). They slow down, stop vibrating violently, and the attractive forces between them take over, turning the gas into a liquid.

• Petroleum gas is subjected to extreme pressure and cooled so it can be filled as a liquid into the red cylinders in your kitchen (LPG - Liquefied Petroleum Gas).
• Hospitals use liquid oxygen, which is created by drastically cooling atmospheric oxygen down to -183°C.