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The recent paper by Treptow (J. Chem. Educ. 1996, 73, 51) on "Free Energy versus Extent of Reaction" covers much the same ground as did my paper in Education in Chemistry, published in 1988. Inevitably, it makes the same point that an essential difference between a reaction involving the interconversion of two solids and one involving two species in a homogeneous phase is that, in the case of the second, there is an important role for the entropy of mixing.
However, with regard to his subsidiary point about the overuse of the symbol Delta, it is not at all clear that Treptow's urgings are well considered. Surely it is enough to say, in regard to either of the reactions mentioned above, that the point of equilibrium will be that where G is a minimum. Thus the first reaction will go to completion but the second will not. Those who are
proficient in the calculus will know that, for the second reaction, the equilibrium state can be identified as that where dG/dx is zero, but that this parameter plays no useful role in regard to the first reaction.
1. Logan, S. R. Educ. Chem. 1988, 25, 44
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