To liquefy a gas like oxygen, we typically need to exert pressure and lower the temperature. However, at room temperature, simply applying enough pressure to oxygen does not result in liquefaction. This is primarily due to the nature of the gas’s intermolecular forces and its critical temperature.
The critical temperature of a substance is the highest temperature at which it can exist as a liquid, regardless of the pressure applied. For oxygen, the critical temperature is about -118.6 degrees Celsius. This means that at room temperature (which is roughly 20 degrees Celsius), oxygen has already surpassed this critical limit.
At temperatures above its critical temperature, oxygen’s molecules have enough kinetic energy that they cannot be forced into a liquid state, even under considerable pressure. Therefore, while increasing pressure does bring molecules closer together, it is not enough to overcome their kinetic energy at higher temperatures. This is why oxygen remains in a gaseous state at room temperature, even when subjected to significant pressure.