Constant pressure, constant temperature reactions are exergonic if and only if the Gibbs free energy change is negative ( " " G " < 0 ) . " Exergonic " ( from the prefix exo-, derived for the Greek word ?? " exM ", " outside " and the suffix-ergonic, derived from the Greek word ???? " ergon ", " work " ) means " releasing energy in the form of work ".
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A favorable reaction is one in which the change in free energy " G?is negative ( exergonic ) or in other words, the free energy of product, G?product, is less than the free energy of the starting materials, G?reactant . " G?> 0 ( endergonic ) corresponds to an unfavorable reaction . " G?can be written as a function of change in enthalpy ( " H?) and change in entropy ( " S?) as "' " G?= " H?T " S?" '.
