Standard states infinitely dilute weight percent

For non-ideal solutions it is sometimes more convenient to use thermodynamic quantities like standard free energy change, activity, activity coefficient, etc.. relative to a standard state other than the pure substance. Henry s law offers two such alternative states infinitely dilute, atom fraction and infinitely dilute, weight percent standard states. 

Infinitely Dilute, Weight Percent Standard State... 

Assuming that the solution obeys Henry s law up to 1 wt % of A, then h is unity at this concentration, and thus the standard state is the 1 wt% solution. Deviations from this equality of activity and weight percent are measured in terms of Henrian activity coefficient relative to the infinitely dilute, weight percent standard state, i.e. 

Though in both the equations (6.27) and (6.30) h and f have been used for denoting the Henrian activity and activity coefficient of A respectively, in Eq.(6.27) they signify relative to the infinitely dilute, atom fraction standard state, while in Eq.(6.30) they are relative to the infinitely dilute, weight percent standard state. 

The free energy change accompanying the transfer of one mole of A from the pure substance standard state to the infinitely dilute, weight percent standard state, i.e. 

The activity coefficient of chromium in iron at infinite dilution relative to pure solid chromium as the standard state is unity. Calculate the change in free energy when solid chromium is dissolved in iron so as to form an infinitely dilute, weight percent solution of chromium in liquid iron at 1800 C (2073K) from the following data ... 

Vanadium melts at 1720°C (1993 K). The Raoultian activity coefficient of vanadium at infinite dilution in liquid iron at 1620°C (1893 K) is 0.068. Calculate the free energy change accompanying the transfer of the standard state from pure solid vanadium to the infinitely dilute, weight percent solution of vanadium in pure iron at 1620°C. 

This convention applies to solutes, for example to salts dissolved in water. The standard state of species i is a solution of concentration Co,i = 1, which has the properties of an infinitely dilute solution. This does not refer to a real physical situation, but rather offers a formalism that is quite useful for the calculation of equilibria in solution. The concentration can be expressed in weight percent, molarity (mole per liter), or molality (mole per kg). 

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