Spontaneous
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Spontaneous
I'm having a hard time trying to conceptually understand when reactions are considered spontaneous, can anyone clarify?
Re: Spontaneous
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.
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.
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Re: Spontaneous
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
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
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Re: Spontaneous
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
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
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Re: Spontaneous
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!
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!
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Re: Spontaneous
Reactions are considered spontaneous when the products are favored over the reactants.
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Re: Spontaneous
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
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
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Re: Spontaneous
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
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Re: Spontaneous
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
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Re: Spontaneous
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.
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Re: Spontaneous
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
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Re: Spontaneous
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.
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