- What is high critical temperature?
Critical temperatures (the maximum temperature at which a gas can be liquefied by pressure) range from 5.2 K, for helium, to temperatures too high to measure. Critical pressures (the vapour pressure at the critical temperature) are generally about 40–100 bars.

- How do you calculate critical temperature and pressure?
Solution: TC = 647 K, PC = 22.09 Mpa = 22.09 × 103 kPa, VC = 0.0566 dm3 mol-1. Therefore, Van der Waals constant, b = VC/3 = (0.0566 dm3 mol-1)/3 = 0.0189 dm3 mol-1. From the critical constants formula of real gas, a = 3 PC VC2 = 3 (22.09 × 103) × (0.0566)2 = 213.3 kPa mol-2.