At high pressure a van der Waals gas has $Z = 1 + \frac{P b}{RT}$ . For a gas at $300 K$ the plot of $Z$ against $P$ in this region has slope $1.60 \times 1 0^{- 3} at m^{- 1}$ . The value of $b$ ( $R = 0.0821 L atm K^{- 1} mo l^{- 1}$ ) is

Answer: B

Slope

= b / RT

, so

b = slope \times RT = 1.60 \times 1 0^{- 3} \times 0.0821 \times 300 = 0.0394 L mo l^{- 1}

, i.e. about

0.0394 L mo l^{- 1}

(close to the value for nitrogen).