Spontaneous






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Ryan Neis 2L
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Spontaneous

Postby Ryan Neis 2L » Thu Feb 01, 2018 6:13 pm

I'm having a hard time trying to conceptually understand when reactions are considered spontaneous, can anyone clarify?

Cooper1C
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Re: Spontaneous

Postby Cooper1C » Thu Feb 01, 2018 6:29 pm

Reactions are spontaneous when delta G is negative.

delta G = delta H - (T * delta S)

Releasing heat is favored, and increasing entropy is favored (for example, liquid to gas - especially favored at higher temperatures). You have to consider both cases to make a conclusion about the spontaneity of a reaction.

Sarah Rutzick 1L
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Re: Spontaneous

Postby Sarah Rutzick 1L » Thu Feb 01, 2018 6:49 pm

Dr. Lavelle gave us guidelines to help determine when a reaction is spontaneous (deltaG is negative):
Positive deltaS and negative deltaH = spontaneous at all temperatures
Positive deltaS and positive deltaH = spontaneous at high temperatures
Negative deltaS and negative deltaH = spontaneous at low temperatures
Negative deltaS and positive deltaH = not spontaneous at any temperatures

William Xu Dis 1D
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Re: Spontaneous

Postby William Xu Dis 1D » Thu Feb 01, 2018 8:58 pm

When delta G is negative, the reaction is spontaneous.

Take a roaring bonfire, for example. This is a spontaneous process because entropy is increasing, and heat is given off by the combustion reactions of the fire. And overall, after the reactants are burned, the products have a lower amount of energy. These factors (delta H and delta S)can make a reaction spontaneous

Guangyu Li 2J
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Re: Spontaneous

Postby Guangyu Li 2J » Fri Feb 02, 2018 5:06 am

Just a suggestion to view question 9.51 on the textbook: Why exothermic reactions are spontaneous?

Exothermic reactions are commonly spontaneous reactions because the result is an increase in the entropy of the surroundings. Using the mathematical relationship △G=△H-T△S, it is pretty clear that if △H is large and negative compared to △S, the reaction will generally be spontaneous because it will result in a negative delta G value

Hope this helps!

Julie Steklof 1A
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Re: Spontaneous

Postby Julie Steklof 1A » Fri Feb 02, 2018 9:54 am

Reactions are considered spontaneous when the products are favored over the reactants.

Adam Enomoto 1L
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Re: Spontaneous

Postby Adam Enomoto 1L » Fri Feb 02, 2018 12:05 pm

Also it’s spontaneous when delta h is negative and delta s is positive

Ashley Garcia 2L
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Re: Spontaneous

Postby Ashley Garcia 2L » Sat Feb 03, 2018 3:44 pm

When △G is negative, the reaction is spontaneous. A spontaneous reaction is one occurs on its own without being driven by an outside force. The products are favored over the formation of the reactants in a spontaneous reaction.

Using the equation △G=△H-T△S:
Positive △S and negative △H = spontaneous at all temps
Positive △S and positive △H = spontaneous at high temps
Negative △S and negative △H = spontaneous at low temps
Negative △S and positive △H = not spontaneous at any temps

Phillip Winters 2F
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Re: Spontaneous

Postby Phillip Winters 2F » Sat Feb 03, 2018 5:56 pm

Reactions are spontaneous when delta G is negative, meaning that the free energy of the products is less than the free energy of the reactants. If you look at a graph of free energy, this makes sense because it does not require energy to go down a hill, meaning that this process is spontaneous, however if delta G was positive, it would require energy to go up the hill, meaning that the process is not spontaneous

Garret G 2F
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Re: Spontaneous

Postby Garret G 2F » Sat Feb 03, 2018 6:53 pm

This video does a really great job of explaining how spontaneity and Gibbs Free Energy are related https://www.youtube.com/watch?v=CHHu-iTwHjg

Yu Chong 2H
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Re: Spontaneous

Postby Yu Chong 2H » Sat Feb 03, 2018 10:15 pm

To add on, spontaneous reactions don't just happen. Spontaneous reactions means that products are at a lower energy level than the reactants. To start the reaction though, you might need activation energy. When the activation energy is supplied, the reaction continues to the end. For example, a spark is needed to ignite gasoline, gas doesn't just burst into flames for no reason.

Kevin Tabibian 1A
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Re: Spontaneous

Postby Kevin Tabibian 1A » Sun Feb 04, 2018 12:05 am

Spontaneous simply means that it can naturally occur without outside influences. It makes sense that because everything in nature attempts to have as low of an energy level as it can, losing free energy ( negative Delta G) will happen naturally

Rohan Chaudhari- 1K
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Re: Spontaneous

Postby Rohan Chaudhari- 1K » Sun Feb 04, 2018 12:09 am

Just to add on, spontaneity refers to the fact that the reaction is favored to occur. An example of this concept would be a boulder on a hill, as it would likely roll down the hill.

Xin He 2L
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Re: Spontaneous

Postby Xin He 2L » Sun Feb 04, 2018 3:06 am

Reactions are spontaneous whenever the delta G of the reaction is a negative value.

Arshpreet Sandhu 1B
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Re: Spontaneous

Postby Arshpreet Sandhu 1B » Sun Feb 04, 2018 9:41 pm

delta G has to be negative in order for a reaction to be considered spontaneous


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