Free energy of formation in solution. Convention concerning hydrates

Free energy of formation in solution. Convention concerning hydrates 

It is useful at this stage to describe one of the important methods of determining the free energy of formation of substances in solution. Consider the equilibrium between a gaseous substance A and its aqueous solution -oin. 

Using the molality scale for the dissolved substance this equilibrium relation may be written 

Since jn° and /e are both independent of the concentration of the particular solution the same applies also to the ratio fjya r The value of this ratio may be determined therefore by plotting measured values of pj a against and extrapolating to infinite dilution where fa Pa- t Now the difference in equation 

In certain instances hydrates are formed, and, if the proportions of hydrate and non-hydrate are unknown, it is convenient to adopt the convention t that the standard free energy of formation refers to an ideal solution in which the total molality is unity. 

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