I find the idea of an exergonic, endothermic reaction quite perplexing, even though I know it is possible, sine delta S is also considered when calculating delta G (hence the reaction ultimately ending up as exergonic) If a reaction takes up heat (a form of energy) as an endothermic reaction then has to release energy as an exergonic reaction, why did it take up the heat in the first place? was the heat used as activation energy?