Need help with a Dr. Collins chem question

[needsomehelpnow]

I am having trouble with this question.

If a reaction is occurs spontaneously, which of the following will increase?

a. internal energy
b. free energy
c. temperature
d. pressure

It says the answer is b. free energy however, I don't understand because in order to be a spontaneous reaction delta G(Gibbs free energy) has to be negative.

I found a thread asking the same question but I don't find the answer convincing

http://forums.studentdoctor.net/showthread.php?t=713959

because the on who answered the question is not taking into account that delta g should be compared with the same reactant and product. when he says that its going to reach equilibrium where delta G = zero, the first delta G (negative) and the second delta G (zero) should be considered a different reaction in terms of internal energy or temperature or whatever. when it reaches equilibrium, the free energy is not increasing. Rather, it's not changing, therefore delta G = 0.

I don't know how to put it clearly but to sum it up,

1st spontaneous step ; free energy decreases (delta G < 0)
2nd equilibrium step ; no change in free energy (delta G = 0 )

Thus, if you compare the product status in step 2 (which is in equilibrium) with the initial reactant in step1, the free energy is decreasing, and even if you compare step2 product with step2 reactant the free energy is zero, which is still not a positive value. Either way, there cannot be an increase in free energy.

Please help.

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[rab86]

I am having trouble with this question.

If a reaction is occurs spontaneously, which of the following will increase?

a. internal energy
b. free energy
c. temperature
d. pressure

It says the answer is b. free energy however, I don't understand because in order to be a spontaneous reaction delta G(Gibbs free energy) has to be negative.

I found a thread asking the same question but I don't find the answer convincing

http://forums.studentdoctor.net/showthread.php?t=713959

because the on who answered the question is not taking into account that delta g should be compared with the same reactant and product. when he says that its going to reach equilibrium where delta G = zero, the first delta G (negative) and the second delta G (zero) should be considered a different reaction in terms of internal energy or temperature or whatever. when it reaches equilibrium, the free energy is not increasing. Rather, it's not changing, therefore delta G = 0.

I don't know how to put it clearly but to sum it up,

1st spontaneous step ; free energy decreases (delta G < 0)
2nd equilibrium step ; no change in free energy (delta G = 0 )

Thus, if you compare the product status in step 2 (which is in equilibrium) with the initial reactant in step1, the free energy is decreasing, and even if you compare step2 product with step2 reactant the free energy is zero, which is still not a positive value. Either way, there cannot be an increase in free energy.

Please help.

The question itself is a little ambiguous because it doesn't talk about system or surroundings but if the answer is B then the only thing that I could assume it's thinking is a reaction is accompanied by the release of of usable energy (delta G being negative). Thus free energy (just G) increases in the surroundings.

 

[bigpapalapagus]

spontaneous is a bit of a misnomer. use product favored instead and it makes more sense. product favored means the product is more stable(less energy). the product is more stable because it is lower in energy and the reactants are less stable with more energy. spontaneous(product favored) reaction is lower in energy(more stable) because energy was released(free energy). sorry this is choppy, I couldn't see the question to answer with better organization.

 

[bigpapalapagus]

The "-"delta G means that energy has left the system, the system lost energy hence a "-", and this energy is now free energy to do what it wants, probably as heat. That is where the increase comes from. The link answer was not a clear answer, try to forget you read it.

 

[needsomehelpnow]

The "-"delta G means that energy has left the system, the system lost energy hence a "-", and this energy is now free energy to do what it wants, probably as heat. That is where the increase comes from. The link answer was not a clear answer, try to forget you read it.

I get your point. Thank you for your help!!