Find the internal pressure `p_i` of a liquid if its density `rho` and specific latent heat of vaporization `q` are known. The heat `q` is assumed to be equal to the work performed against the forces of the internal pressure, and the liquid obeys the Van der Waals equation. Calculate `p_i` in water.

Explanation

The internal pressure being `(a)/(V^2)`, the work done in condensation is
`int_(V_l)^(V_s) (a)/(V^2) dV = (a)/(V_l) - (a)/(V_g) ~~ (a)/(V_l)`
This by assumption is `Mq, M` being the molecular weight and `V_l, V_g` being the molae volumes of the liquid and gas.
Thus `p_l = (a)/(V_l^2) = (Mq)/(V_l) = rho q`
where `rho` is the density of the liquid . For water `p_i ~~ 3.3 xx 10^13 atm`.