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Homework Help: Gibbs Energy

  1. Mar 5, 2015 #1
    1. The problem statement, all variables and given/known data
    Will the following processes be spontaneous only at high temperatures, only at only temperatures, at all temperatures, or at no temperatures?


    2. Relevant equations

    3. The attempt at a solution
    So i just need to figure out how to predict the sign of Delta(S) but im not sure how to do that with just the balanced equation given, any tips would be helpful.

  2. jcsd
  3. Mar 5, 2015 #2
    I think this question is referring to the effect of temperature on the equilibrium constant. For an exothermic reaction (negative delta H), does the equilibrium constant increase with temperature or decrease with temperature?

  4. Apr 9, 2015 #3
    The total moles in the reactants are more than the products. This is decreasing entropy. If the total moles were more in the products, then this would be increasing entropy. So, when ΔH is negative, and ΔS<0 (decreasing entropy), we know that this is spontaneous at low temps.

    The trends are as follows:
    ΔS>0 and ΔH<0 Spontaneous (ΔG<0)
    ΔS>0 and ΔH>0 spontaneous at high temps.
    ΔS<0 and ΔH<0 spontaneous at low temps
    ΔS<0 and ΔH>0 non-spontaneous (ΔG>0)

    Notice that when the signs for both ΔS and ΔH are the same, it dictates the conditions of the reaction (H and S <0 are both spont. at low temps) and (H and S>0 are spont. at high temps). Hope this helps.
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