When we refer to the equilibrium vapor pressure of a liquid, we tacitly assume
that some of the liquid has evaporated into a vacuum and that equilibrium is
then achieved. Suppose, however, that we are able by some means to exert an
additional pressure on the surface of the liquid. One way to do this is to
introduce an insoluble, inert gas into the space above the liquid. In this
problem, we will investigate how the equilibrium vapor pressure of a liquid
depends upon the total pressure exerted on it.
Consider a liquid and a vapor in equilibrium with each other, so that
\(\mu^{\prime}=\mu^{8}\). Show that \(\bar{V}^{1} d P^{1}=\bar{V}^{g} d P^{8}\)
because the two phases are at the same temperature. Assuming that the vapor
may be treated as an ideal gas and that \(\bar{V}^{1}\) does not vary
appreciably with pressure, show that \(\ln \frac{P^{\S}\left(\text { at }
P^{1}=P\right)}{P^{8}\left(\text { at } P^{1}=0\right)}=\frac{\bar{V}^{1}
P^{1}}{R T}\) Use this equation to calculate the vapor pressure of water at a
total pressure of 10.0 atm at \(25^{\circ} \mathrm{C} .\) Take
\(P^{\mathrm{g}}\left(\text { at } P^{1}=0\right)=0.0313 \mathrm{atm}\).