## Exothermic and Spontaneous

isochoric/isometric: $\Delta V = 0$
isothermal: $\Delta T = 0$
isobaric: $\Delta P = 0$

Megan Purl 1E
Posts: 49
Joined: Fri Sep 29, 2017 7:07 am

### Exothermic and Spontaneous

What is the difference between exothermic and spontaneous? Are all exothermic reactions spontaneous and are there times when endothermic reactions are spontaneous?

Julia Ward 2C
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Joined: Wed Nov 16, 2016 3:03 am

### Re: Exothermic and Spontaneous

An exothermic reaction is when a reaction has a net release of heat, system loses heat (ΔH is negative). Spontaneous means that the reaction happens without any added help (ie. any extra energy). Spontaneous reactions have a negative ΔG. So exothermic and endothermic reactions can be spontaneous depending on the value of TΔS (Remember ΔG=ΔH-TΔS).
Last edited by Julia Ward 2C on Sun Feb 04, 2018 10:42 pm, edited 2 times in total.

Rachel Formaker 1E
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### Re: Exothermic and Spontaneous

Exothermic and endothermic refer to ΔH, or the amount of heat absorbed or released in a reaction.
Spontaneous and non-spontaneous refer to ΔG, or the free energy change of the reaction.

Because ΔG = ΔH - TΔS, ΔG depends on both ΔH and ΔS.
So not all exothermic reactions (ΔH < 0) will be spontaneous (ΔG < 0), and not all endothermic reactions (ΔH > 0) will be non-spontaneous (ΔG > 0), since you need to know both ΔH and ΔS to find ΔG.

Jared Smith 1E
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Joined: Fri Sep 29, 2017 7:04 am

### Re: Exothermic and Spontaneous

I think that the difference between the two is that exothermic means that deltaH is negative, and that spontaneous means that deltaG is negative. So that means that exothermic relates to enthalpy and that spontaneity relates to Gibbs Free Energy. I think that there are some situations that an exothermic reaction is nonspontaneous, like when entropy has a negative value. So I think, in answering your question, no, they are not the same thing.

Ethan Vuong 3G
Posts: 51
Joined: Fri Sep 29, 2017 7:07 am

### Re: Exothermic and Spontaneous

I believe that you can have a spontaneous endothermic such as melting ice.