Find the entropy increment of one mole of a Van der Waals gas due to the isothermal variation of volume from `V_1` to `V_2`. The Van der Walls corrections are assumed to be known.

Explanation

For a Vander Waal gas
`(p + (a)/(V^2))(V - b) = RT`
The entropy change along an isotherm can be calculated from
`Delta S = int_(V_1)^(V_2) ((del S)/(del V))_T dV`
If follows from (2.129) that
`((del S)/(del V))_T = ((del p)/(del T))_V = (R)/(V - b)`
Assuming `a,b` to be known constants.
Thus `Delta S = R 1n (V_2 - b)/(V_1 - b)`.