Question

We can liquefy oxygen and nitrogen gas but not carbon dioxide . WHY ???

Answer 1

We CAN liquefy carbon dioxide!

Explanation:

However, we can't liquefy carbon dioxide if the pressure is less than 5.2 atm.

That's because the attractive forces between the molecules are too weak to overcome the kinetic energy of motion.

If the temperature gets cold enough, the carbon dioxide deposits as a solid rather than condense to a liquid.

We can liquefy carbon dioxide if the pressure is greater than 5.2 atm (530 kPa or 5.3 bar) and the temperature is less than 31 °C.

The molecules are then close enough together, and the kinetic energies are small enough that the substance can form a liquid.

In the video below, watch the solid carbon dioxide melt as the pressure exceeds 500 kPa.