Question

For a real gas obeying Van der Waals equation, a graph is plotted between $P{V}_m$ (y-axis) and P(x-axis) where $V_m$ is molar volume. Find y-intercept of the graph.

Answer 1

$(P+\frac{a{n}^2}{V^2})(V-nb)=nRT$ for ${}^{\prime }{n}^{\prime }$ moles.

where a and b are Van der Waals constants.

The constant 'a' measures the forces of attraction between the molecules of the gas and 'b' relates to the volume of the molecules, measuring the size of the gas molecules.

For $n=1$,

$PV=Pb-\frac{a}{V}+\frac{ab}{V^2}+RT$

It is in the form $y=mx+c$

where $c$ is Y - Intercept.

Y - Intercept: $\frac{a}{V}-\frac{ab}{V^2}+RT$