Question
van der Waal’s equation for a gas is stated as, $$P = \frac{{nRT}}{{V - nb}} - a{\left( {\frac{n}{V}} \right)^2}.$$
This equation reduces to the perfect gas equation, $$P = \frac{{nRT}}{V}$$ when,
A.
temperature is sufficient high and pressure is low.
B.
temperature is sufficient low and pressure is high.
C.
both temperature and pressure are very high.
D.
both temperature and pressure are very low.
Answer :
temperature is sufficient high and pressure is low.
Solution :
$$\eqalign{
& {\text{Given}}\,\,P = \frac{{nRT}}{{v - nb}} - a{\left( {\frac{n}{v}} \right)^2} \cr
& {\text{Which can also be written as}} \cr
& \left[ {P + \frac{{{n^2}a}}{{{V^2}}}} \right]\left( {V - nb} \right) = nRT \cr} $$
At low pressure and high temperature the effect of $$\frac{a}{{{V^2}}}$$ and $$b$$ is negligible hence $$PV = nRT.$$