The critical constants of a gas are $T_{c} = 400 K$ , $P_{c} = 50 atm$ and $V_{c} = 0.20 L mo l^{- 1}$ . Its experimental critical compressibility factor ( $R = 0.0821 L atm K^{- 1} mo l^{- 1}$ ) is closest to

Answer: A

Z_{c} = \frac{P _{c} V _{c}}{R T _{c}} = \frac{50 \times 0.20}{0.0821 \times 400} = \frac{10}{32.84} = 0.305

, closest to 0.30. This is below the van der Waals value 0.375, as is typical of real gases.