On the use of ΔQ° rather than T°ΔS° in the calculation of ΔG° accompanying the oxidation or fermentation of catabolic substrates of biological importance in their standard states

The purpose of this study has been to determine the effect of substituting ΔQ° for T°ΔS° in the Gibbs free energy equation (ΔG°=ΔH°−T°ΔS°, ) so that ΔG°ΔQ=ΔH°−ΔQ° (). The result is that values of ΔcG°ΔQ averaged 1.04±0.01 (n=5) times more negative than those of ΔcG° for the bomb calorimetric oxidations of five liquid catabolic substrates, with a range 1.02–1.06. Values of ΔcG°ΔQ averaged 1.03±0.01 (n=17) times more negative than those of ΔcG° for 17 theoretical bomb calorimetric oxidations of solid catabolic substrates, with a range 1.02–1.05 . While significant, these differences are not large because in bomb calorimetric oxidations the values of T°ΔcS° and ΔcQ° are small compared to those of ΔcH°. On the other hand, for six fermentations values of T°ΔpS° and ΔpQ° are much larger compared to values of ΔpH° than those for oxidations. Here, values of ΔpG° showed wide variations from ΔpG°ΔQ, ranging from 4.88 times greater to 0.88 times less. Clearly, the whole approach to making these calculations using is fundamentally different and significant to the extent given above. The difference between the use of is not trivial. represents a different interpretation of the method of calculating the change in the quantity of absorbed thermal energy exchanged by an irreversible system such as a growth process as it passes from an initial to a final state. It is certainly more simple. It may be more correct. Because ΔG°ΔQ is not the same as ΔG°, it is suggested that the ΔG°ΔQ term in be changed to ΔX°, this letter not being previously used in biological thermochemistry, so that ΔX°=ΔH°−ΔQ°.