Factors Affecting the Sign of ΔG in the Relationship ΔG = ΔH – TΔS
An example spontaneity table, from American chemist Raymond Chang's 1998 Chemistry textbook, showing how the variables ΔH and ΔS are the key to the understanding of reaction spontaneity, as defined by the function "ΔH – TΔS". [2]

Factors Affecting the Sign of ΔG in the Relationship ΔG = ΔH – TΔS

An example spontaneity table, from American chemist Raymond Chang's 1998 Chemistry textbook, showing how the variables ΔH and ΔS are the key to the understanding of reaction spontaneity, as defined by the function "ΔH – TΔS". [2]

In equations, the function:

$\Delta H - T \Delta S \,$

is called the "free energy content change", or available energy change, of a closed isothermal-isobaric freely-going process and is the thermodynamic expression of Gibbs free energy change ΔG, and is the change of enthalpy ΔH less the conjugate energy pair of the product of the absolute temperature T of the system and the entropy change of the system ΔS, a quantity, TΔS, otherwise known as bound energy.

Thims
American electrochemical engineer Libb Thims spent a period of at least six years studying this quantity, from 1995 to 2001, as a sort of pastime hobby, during which period the "ΔH – TΔS" expression was viewed as essentially a black box as to how the changes of the three variable of this expression relate to states of human existence, such as on going from the “single state” to the “married with 2.5 kids state”. [1]

One of the precipitates of this effort was the publication of the two-volume 2007 textbook Human Chemistry, the first-ever attempt to ferret out the basic structure of the science of human chemistry.

References
1. Thims, Libb. (2007). Human Chemistry (Volume Two) (pgs. 668-72. Morrisville, NC: LuLu.
2. Chang, Raymond. (1998). Chemistry (pg. 740). McGraw-Hill.

External links
● Why does ΔH – TΔS equal “useful” energy? (2009) – Yahoo Answers.