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

I know the answer but I can't understand why


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Most Helpful Girl

  • 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).

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What Guys Said 2

  • 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.

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  • Chemistry?

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

    • Thermonuclear? In what case exactly

What Girls Said 1

  • 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

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