## Exothermic reactions

$\Delta G^{\circ}= \Delta H^{\circ} - T \Delta S^{\circ}$

$\Delta G^{\circ}= -RT\ln K$

$\Delta G^{\circ}= \sum \Delta G_{f}^{\circ}(products) - \sum \Delta G_{f}^{\circ}(reactants)$

605136321
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### Exothermic reactions

Why are so many exothermic reactions spontaneous?

Eugene Chung 3F
Posts: 142
Joined: Wed Nov 15, 2017 3:03 am

### Re: Exothermic reactions

All spontaneous processes have an increase in entropy. In other words, heat will always flow from hot to cold and never cold to hot spontaneously. So, S(universe) >0 for spontaneous process (2nd law of thermo.). We also know that delta H is negative for exothermic reactions and that delta G = delta H - T*delta S. So, H will be negative and S will be positive. Thus, G will be negative and spontaneous.

Ruby Richter 2L
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Joined: Thu Jul 25, 2019 12:17 am

### Re: Exothermic reactions

What exactly does it mean for a reaction to be spontaneous? I know it involves an increase in entropy but what are other determinants?

rohun2H
Posts: 100
Joined: Wed Sep 18, 2019 12:19 am

### Re: Exothermic reactions

Lavelle briefly mentioned determining spontaneity at the beginning of thermo but I believe he'll be explaining this concept sometime this week.

805422680
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### Re: Exothermic reactions

Spontaneous processes have an increase in entropy. Delta H will be negative and S will be positive. Therefore G will be negative and hence the process is spontaneous

Vicki Liu 2L
Posts: 101
Joined: Sat Aug 24, 2019 12:15 am

### Re: Exothermic reactions

Conceptually, it makes sense for exothermic reactions to be spontaneous as the release of energy makes the system more stable. Endothermic reactions on the other hand require an input of energy and thus, are not naturally occurring.