Chemical Thermodynamics

Chapter 12

Aqueous Solutions of Electrolytes

12.a.  Fugacity and Activity of Electrolytes

Gaseous systems and solutions of non-electrolytes behave almost ideally at very low concentrations. Solutions of electrolytes, however, exhibit marked deviations from ideal behaviour even at very low concentrations. An aqueous solution of an electrolyte contains the constituent ions and so electrolytes as solutes are treated separately from the non-electrolyte solutes. The standard state for a solute is usually chosen based on a plot of its fugacity (f₂) against its molality (m₂). The limiting slope is determined as m₂ → 0. This limiting slope extrapolated to m₂ = 1 gives the value of the Henry’s law constant, K. The standard state is so chosen that However, ...