Question

At low pressure, the van der Waal's equation is reduced to

• A. $Z=\frac{PV_{m}}{RT}=1-\frac{a}{VRT}$
• B. $Z=\frac{PV_{m}}{RT}=1+\frac{b}{RT}P$
• C. $PV_{m}=RT$
• D. $Z=\frac{PV_{m}}{RT}=1-\frac{a}{RT}$

Answer 1

Answer: (A)

When pressure is low
$\left[P+\frac{a}{V^{2}}\right]\left(V-b\right)=RT$
or $PV=RT+Pb-\frac{a}{V}+\frac{ab}{V^{2}}$
or $\frac{PV}{RT}=1-\frac{a}{VRT}$
$Z=-\frac{a}{VRT}$
$\left(\because\frac{PV}{RT}-Z\right)$