Equilibrium of a Flat Water Solution

Let us consider a water solution (flat surface) at constant temperature T and pressure p in equilibrium with the atmosphere. Water equilibrium between the gas and aqueous phases requires equality of the corresponding water chemical potentials in the two phases (see Chapter 10) [Pg.766]

Water vapor behaves in the atmosphere as an ideal gas, so its gas-phase chemical potential is [Pg.766]

This equation describes the behavior of the system for any solution composition. Note that the right-hand side (RHS) is a function of temperature only and therefore will be equal to a constant, K, for constant temperature. Considering the case of pure water (no solute) we note that when x , = 1, yw 1 and p° = p° = K(T), where p° is the vapor pressure of water over pure water. Therefore (17.13) can be rewritten as [Pg.767]

Equation (17.14) is applicable for any solution and does not assume ideal behavior. Nonideality is accounted for by the activity coefficient yw. [Pg.767]

The mole fraction of water in a solution consisting of nw water moles and ns solute moles is given by [Pg.767]

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