1. Concentration and supersaturation

1.1 Concentration units and activity in solution

To express solute content, we use the classic definitions of concentrationC, mass fraction (sometimes expressed in g/100 g solution) and mole fraction.

For electrolyte solutions, it is not always sufficient to use concentrations, as thermodynamics requires the use of activitiesa _i . These are in fact concentrations (expressed in moles per liter) multiplied by a certain coefficient called the activity factor (f _i ), so that for any species i :