"True or false: exothermic reactions are always spontaneous. Explain why." ?

[Anonymous]

I know the answer but I can't understand why

[BarbaraP]

False. Exothermic reactions release energy, while endothermic reactions require energy. It may seem that it's easier to activate a reaction that releases energy, but that's not enough to estabilish if it will be spontaneous or not. The spontaneousity of a reaction depends on Gibbs free energy which is a function of entropy and enthalpy (G= H - TS). If DG is <0 the reaction will be termodynamically favored. So you will need both entropy and enthalpy to estabilish the spontaneousity, not just enthalpy (which tells us if a reaction is endothermic or exothermic).

[BarbaraP]

Thanks for MHO

[Jrizzy]

That's not true. Heat is released when the acids of a battery create electrical energy right? That's pretty deliberate since it was designed to do that

[ClassicRocker]

They are not always spontaneous. In an exothermic reaction in which the entropy change is also negative the reaction may not always be spontaneous.
Therefore, since I have given you an example of at least on case in which the reaction is not spontaneous exothermic reactions cannot be considered "ALWAYS" spontaneous.

[Omar5881]

Chemistry?

[Asker]

I think so, but I'm studying this stuff in physics

[Omar5881]

Thermonuclear? In what case exactly