What is the difference between endergonic reactions and
endothermic reactions? Exergonic and exothermic? The terms seem to be very similar, but
not identical; is there a difference?
Endergonic and exergonic refer to free energy changes (delta G). Endothermic and
exothermic refer to the changes in internal energy of molecules, measured as heat given
off or taken up, delta H. Delta G takes into account not only changes in internal energy
but also changes in entropy (delta S) that may accompany a reaction. For most ordinary
simple chemical reactions, the entropy factor is not great, so chemists usually talk about
delta H. For many biological reactions,the entropy factor is significant, so biochemists
usually talk about delta G. Delta G = delta H - (T x delta S ). Despite the signs, which
have to do with the way these terms are defined, delta G is the sum of the 2 effects.
Becker presents this very nicely. You may forget about delta H for this course. More in a
later lecture.