Interpretation of Logarithmic Term. Molality

1 The Nature of Logarithmic Terms in Chemical Potential Equations 

It is necessary here to digress briefly in order to introduce the term molality which is required for the definition of an ideal dilute solution (section 36.3 below). The molality of a component, i, in a solution, mi, is defined as the amount of the solute, i, in 1 kg (= 1000 g) of solvent. 

Thus for a solute, labelled A, in a solvent, labelled B, the molality, mA is given by  

Since water as a solvent has a density of 1 g cm-3 then 1000 g of water has a volume of exactly 1 dm 3 and hence the concentration, c, (Frame 40, section 40.3) of a substance, i, in water (in mol dm 3) will be identical to its molality (in mol kg-1) at a temperature of 298 K. This will not be true, of course  

3 Chemical Potentials for Ideal Dilute Solutions at Equilibrium 

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