ABSTRACT
In Chap. 8 it was seen that the absence of interatomic forces between the atoms of ideal gases causes the heat of mixing of ideal gases to be zero. This situation represents one extreme of a range of possible situations. Toward the other extreme of this range is the situation in which gases which exhibit marked chemical affinity for one another are mixed. For example, considerable heat is released when gaseous hydrogen and oxygen are mixed in the presence of a catalyst. The thermodynamics of such a system can be treated in either of two ways. The mixture can be considered to be a highly nonideal mixture of H2 and O2, the thermodynamic equilibrium state of which, at given temperature and pressure, can be defined in terms of the fugacities of the components H2 and O2; or it can be considered that the H2 and O2 have reacted with one another to some extent to produce the product species H2O. In the latter case, if the pressure of the system is low enough, the equilibrium state at the given temperature can be defined in terms of the partial pressures exerted by the three species, H2, O2, and H2O, occurring in the system. Although both treatments are thermodynamically equivalent, the latter, by virtue of its correspondence with physical reality, is by far the more convenient and practical.
