## Spontaneous Reaction

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

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

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

Semi Yoon
Posts: 60
Joined: Fri Sep 28, 2018 12:27 am

### Spontaneous Reaction

Why would the precipitation of snowflakes inside a cloud at -10C and 0.839 atm be a spontaneous reaction?

GavinAleshire1L
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Joined: Fri Sep 28, 2018 12:21 am

### Re: Spontaneous Reaction

I was confused by the same question. How do we interpret delta G without knowing the magnitude of delta H and T delta? Is there a way to use pressure to help solve?

Cole Doolittle 2K
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### Re: Spontaneous Reaction

I am also confused. I understand that delta H would be negative if you are freezing and thus losing heat, but wouldn't delta S also be negative if you are losing entropy going from a liquid to a solid? Thanks in advance!

Pritish Patil 1K
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Joined: Fri Sep 28, 2018 12:24 am

### Re: Spontaneous Reaction

I'm not completely sure. But I assumed that because it is precipitation, the water is going from liquid to solid state. Because the freezing point of liquid water was 0 degrees C, I assumed that the precipitation would be spontaneous as the surrounding temperature was -10 degrees C, which is less than the freezing point.

Noah Fox 1E
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Joined: Fri Sep 28, 2018 12:20 am

### Re: Spontaneous Reaction

I don't think this is the way to answer the question but something that helps me conceptualize it is that heat diffuses out. If a sample of water is in a 10 degree Celsius space, heat leaves the sample and the bonds form spontaneously because of the conditions it is in.

yuetao4k
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### Re: Spontaneous Reaction

I thought of it as a spontaneous reaction because when the temperature is -10 degrees C, then snow precipitating is spontaneous, thus delta G is negative.