Why can't a gas be liquefied by simply pressurizing?
This is mainly because it depends on the temperature of the gas. When the temperature of the gas is relatively high, this temperature is called the critical temperature. At this point, the gas cannot be liquefied, no matter how much pressure it is.
Gases have larger molecular spacing and less interaction forces as compared to liquids and solids. When we simply increase the pressure of the gas, the interaction between these gas molecules does not change. Conversely, as the pressure increases, the repulsive force between the gas molecules also becomes stronger as they are closer together, resulting in the gas molecules not being able to get close to each other, forming a liquid.
If we want to liquefy gas, we need to do so at the right temperature and pressure. Temperature is very important because at low temperatures, the kinetic energy of the gas molecules decreases, enhancing the interaction between them. When the pressure increases to a certain extent and the temperature decreases to the corresponding critical point, the kinetic energy of the gas molecules will not be able to overcome the force of attraction between the molecules, so that the gas molecules gradually come together to form a liquid.
To do this, liquefiing the gas needs to be carried out under the appropriate temperature and pressure conditions to overcome the mutual repulsion between the gas molecules and make it into a liquid state. The liquefaction of the gas is not enough to simply increase the pressure. The liquefaction of the gas can only be achieved after reaching a certain temperature and pressure.