Question

The van der Waals equation for one mole of a real gas at low pressure is

• A. $PV=RT-\frac{a}{V}$
• B. $PV=Pb+RT$
• C. $PV=RT-Pb$
• D. $PV=RT+\frac{a}{V}$

Answer 1

Answer: (A)

$\left(P+\frac{a}{V^2}\right)\left(V-b\right)=RT$
At low $P,V$ is large
$V-b\approx V$
$\left(P+\frac{a}{V^2}\right)\left(V\right)=RT$
$\Rightarrow PV+\frac{a}{V}=RT$
$PV=RT-\frac{a}{V}$