The volume occupied by 1 mole of gas at critical temperature and pressure is called critical volume.
When we talk about critical temperature, it is a term used to define the temperature of a substance above which the vapour of that substance cannot be liquefied irrespective of the amount of pressure you apply. It is very important to know that every substance has a critical temperature and you need to keep that in mind while experimenting with substances.
With the knowledge of what critical temperature is, we can now define critical pressure. At the critical temperature, the vapour phase and the liquid phase of the substance coexist, now at the phase equilibrium curve, the pressure at that point is termed as the critical pressure. We can learn this from the pressuretemperature graph too.
After understanding both critical temperature and critical pressure, we can now learn about critical volume. The molar volume of a gas at critical pressure and critical temperature is called the critical volume. The state at which this happens is called the critical state.
The expression for critical volume is .
Final answer:
The volume occupied by 1 mole of gas at critical temperature and pressure.