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# Thermodynamics watch

1. I really need your opinion in this one:

I think it is meant to be delta G at standard conditions (not sure). So I calculated delta G and it's negative so option A? I think it's either A or B

Many thanks. Help will be appreciated
2. (Original post by Daniel Atieh)
I really need your opinion in this one:

I think it is meant to be delta G at standard conditions (not sure). So I calculated delta G and it's negative so option A? I think it's either A or B

Many thanks. Help will be appreciated
Without an equation it certainly cannot be determined ...

Option D
3. (Original post by charco)
Without an equation it certainly cannot be determined ...

Option D
The equation is
deltaG= delta Gْ + RTln ([products]/[reactants])
4. (Original post by Daniel Atieh)
The equation is
deltaG= delta Gْ + RTln ([products]/[reactants])
I meant the equation for the reaction ...
5. (Original post by charco)
I meant the equation for the reaction ...
hmm I really don't know. But the reaction is feasible, and we have the concentrations. Lets suppose i have the equation, how i should go about solving it?
6. (Original post by Daniel Atieh)
hmm I really don't know. But the reaction is feasible, and we have the concentrations. Lets suppose i have the equation, how i should go about solving it?
Which reaction? There is none stated!
7. (Original post by charco)
Which reaction? There is none stated!
I would assume this (didn't check the image, sorry):

A + B <--> C + D
8. (Original post by Daniel Atieh)
I would assume this (didn't check the image, sorry):

A + B <--> C + D
If it is that equation, and its an equilibrium, then at equilibrium ∆G = 0 so ∆G° = -RT lnK and you can work out the equilibrium ratios. Then just decide whether [A] and [B] will increase or decrease to get to that ratio. (That is assuming the ∆G you've been given is in fact ∆G°. If its ∆G instead, you don't have enough information. I don't really trust the notation of whoever gave you the question though!)
9. (Original post by KombatWombat)
If it is that equation, and its an equilibrium, then at equilibrium ∆G = 0 so ∆G° = -RT lnK and you can work out the equilibrium ratios. Then just decide whether [A] and [B] will increase or decrease to get to that ratio. (That is assuming the ∆G you've been given is in fact ∆G°. If its ∆G instead, you don't have enough information. I don't really trust the notation of whoever gave you the question though!)
Hey

Yes, I confirmed it is delta G at standard conditions. I am given the concentration of each species in the question (1M A, 1M B, 0.1 M C, 0.1 M D).
So shall I calculate delta G? If so, I got a large negative value, and accordingly, can I say it goes in forward direction? Is this approach correct?

I still feel pretty weak at grasping what's going on in this question :/
10. (Original post by Daniel Atieh)
Hey

Yes, I confirmed it is delta G at standard conditions. I am given the concentration of each species in the question (1M A, 1M B, 0.1 M C, 0.1 M D).
So shall I calculate delta G? If so, I got a large negative value, and accordingly, can I say it goes in forward direction? Is this approach correct?

I still feel pretty weak at grasping what's going on in this question :/
My take on this is that the easiest way to tackle it is to use:

ΔG = -RTlnK

To work out K

Then plug in the values given to find out the reaction quotient K'

If K' is larger than K the reaction goes in reverse and vice versa.
11. (Original post by charco)
My take on this is that the easiest way to tackle it is to use:

ΔG = -RTlnK

To work out K

Then plug in the values given to find out the reaction quotient K'

If K' is larger than K the reaction goes in reverse and vice versa.
(Original post by KombatWombat)
If it is that equation, and its an equilibrium, then at equilibrium ∆G = 0 so ∆G° = -RT lnK and you can work out the equilibrium ratios. Then just decide whether [A] and [B] will increase or decrease to get to that ratio. (That is assuming the ∆G you've been given is in fact ∆G°. If its ∆G instead, you don't have enough information. I don't really trust the notation of whoever gave you the question though!)
Many thanks both of you. I utterly got what you mean, and it worked well.

My last question is whether I can simple find delta G and according to that I can decide which side it will favour. In our example, it is negative so forward. What do you think?
12. (Original post by Daniel Atieh)
Many thanks both of you. I utterly got what you mean, and it worked well.

My last question is whether I can simple find delta G and according to that I can decide which side it will favour. In our example, it is negative so forward. What do you think?
But you are given ΔG in the question!
13. (Original post by charco)
But you are given ΔG in the question!
Delta G at standard conditions.
14. (Original post by Daniel Atieh)
Delta G at standard conditions.
The value of ΔG changes during the reaction.

Do you mean to find ΔG at the beginning of the reaction with only A and B present in stoichiometric amounts? (Don't forget that temperature does not feature in standard conditions)

I don't see how this is relevant for your question.
15. (Original post by charco)
The value of ΔG changes during the reaction.

Do you mean to find ΔG at the beginning of the reaction with only A and B present in stoichiometric amounts? (Don't forget that temperature does not feature in standard conditions)

I don't see how this is relevant for your question.
Yes, at that point where we have 1 molar of reactants and 0.1 molar of products. I can calculate delta G for that point and see whether it will occur or not. As I got a negative value, it is feasible and will go towards products. Correct?

I got your point that delta G changes in the course of the reaction, yeah.
16. (Original post by Daniel Atieh)
Yes, at that point where we have 1 molar of reactants and 0.1 molar of products. I can calculate delta G for that point and see whether it will occur or not. As I got a negative value, it is feasible and will go towards products. Correct?

I got your point that delta G changes in the course of the reaction, yeah.
According to your question the reaction will not start under standard conditions from the reactants A & B

ΔG is positive.

But you know that at equilibrium ΔG = 0

Use the standard ΔG value to work out the equilibrium constant

And do your calculations using the molar amounts given to find the quotient = [C][D]/[A][ B]
17. (Original post by charco)
According to your question the reaction will not start under standard conditions from the reactants A & B

ΔG is positive.

But you know that at equilibrium ΔG = 0

Use the standard ΔG value to work out the equilibrium constant

And do your calculations using the molar amounts given to find the quotient = [C][D]/[A][ B]
Thank you. Yes, I got this approach and it worked, but I am still keen to know whether the other pathway makes sense or not.

deltaG= delta Gْ + RTln ([products]/[reactants])
delta G = (0.4 Kj x 10^3) + [8.314 J/K/mol x 298 K x ln (0.1 x 0.1)/1)] = -11000 J

Sorry for disturbance, but it is important for me to know why the above method does/doesn't work

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