Equilibrium Problem: Relationship Between Q, K, and ∆G

[patrickbotros]

I just took a test today, and I want to see if I got the right answer. I sort of guessed. Here's the question:
Which statement is correct?

• a) When Q<K, then ∆G=1
• b) When Q<K, then ∆G=-∆S
• c) When Q=K, then ∆G=0
• d) When Q>K, then ∆G=1
• e) When Q>K, then ∆G=-RT

I put C, because when Q=K, the system is at equilibrium. I don't really know what ∆G is though other than that it's Gibb's Free Energy. Please explain your answer. Thanks so much!

 

[proton007007]

Its correct . change in gibbs free energy becomes zero when equilibrium is attained

 

[patrickbotros]

Its correct . change in gibbs free energy becomes zero when equilibrium is attained

Thanks! While I've got you, would you mind answering this one:
The reaction 2H₂O₂(g) ⇔ 2H₂O(g)+O₂(g) is exothermic: ∆H˚_rxn=-210 kj/mol. Which one of the following is correct:
a) K_p at 800˚K is smaller than K_p at 1,200˚K
b) Temperature does not affect K_p
c) K_p depends only on pressure
d) K_p at 1,200˚K is smaller than K_p at 800˚K
e) K_p depends on total pressure as well as temperature.

 

[proton007007]

But its better to know the reason as luck and logical reasoning may not always help you . Google up Gibbs Free Energy :)

 

[patrickbotros]

But its better to know the reason as luck and logical reasoning may not always help you . Google up Gibbs Free Energy :)

While I've got you, would you mind answering this one:
The reaction 2H2O2(g) ⇔ 2H2O(g)+O2(g) is exothermic: ∆H˚rxn=-210 kj/mol. Which one of the following is correct:
a) Kp at 800˚K is smaller than Kp at 1,200˚K
b) Temperature does not affect Kp
c) Kp depends only on pressure
d) Kp at 1,200˚K is smaller than Kp at 800˚K
e) Kp depends on total pressure as well as temperature.

 

[proton007007]

Well , giving out the answer directly won't do you good and it would (maybe) be against the forum rules . Think about Le Chateliers principle and the temperature variation of equilibrium constant . You must have surely learned this .

 

[patrickbotros]

Well , giving out the answer directly won't do you good and it would (maybe) be against the forum rules . Think about Le Chateliers principle and the temperature variation of equilibrium constant . You must have surely learned this .

I attempted that and I'm just seeing if I was right. I said that D was the answer, because at 1200˚K, more reactants will be produced (exothermic), so Kc would be smaller.

 

[proton007007]

I don't see you mentioning your answer and your attempt above . Anyway , your answer is correct .