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

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  1. Feb 18, 2015 #1
    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!!!!!! :smile::biggrin:
     
  2. jcsd
  3. Feb 18, 2015 #2
    Its correct . change in gibbs free energy becomes zero when equilibrium is attained
     
  4. Feb 18, 2015 #3
    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) 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.
     
    Last edited: Feb 18, 2015
  5. Feb 18, 2015 #4
    But its better to know the reason as luck and logical reasoning may not always help you . Google up Gibbs Free Energy :)
     
  6. Feb 18, 2015 #5
    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.
     
  7. Feb 18, 2015 #6
    Well , giving out the answer directly wont 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 learnt this .
     
  8. Feb 18, 2015 #7
    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.
     
  9. Feb 18, 2015 #8
    I dont see you mentioning your answer and your attempt above . Anyway , your answer is correct .
     
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