Concise discussion on reaction equilibrium

In the previous section the special case of the reaction A was discussed. We shall continue to suppose that only a single reaction takes place in the system, but it will now be written in the generalized 

The negative of the quantity ZviPi has been called by de Donder the affinity of the reaction. As is evident from the discussion near the end of 4 3, the afSnity must be positive if the reaction is to proceed spontaneously from left to right of the chemical equation as usually written, and it must be negative for reaction in the reverse direction. 

The condition of chemical equilibrium is obtained by minimizing O with respect to at constant temperature and pressure, i.e. by 

This is the most general condition of the equilibrium of a single reaction and is applicable whether the reactants and products are solids, liquids or gases. It is to be noted that it is obtained from the chemical equation (4 7) simply by replacing each chemical formula by the corresponding chemical potential. 

---