It can be advantageous to describe the aqueous phase in terms of molality instead of concentration. The molality of a solution does not change with T , since it refers to the mass of the solvent. In contrast, the concentration c does change with T , since the density of a solution and thus its volume are temperature-dependent. Defining the aqueous-phase composition via molality has the advantage that any temperature dependence of the Henry's law constant is a true solubility phenomenon and not introduced indirectly via a density change of the solution. Using molality, the Henry solubility can be defined as