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Homework Help: Enthalpy/Entropy question. Br2 liquid to 2Br gas

  1. Nov 9, 2009 #1
    1. The problem statement, all variables and given/known data
    Br2 (l) --> 2Br (g)

    the options are:

    a. H is positive and S is positive for the reaction
    b. H is negative and S is positive for the reaction
    c. H is positive and S is negative for the reaction
    d. H is negative and S is positive for the reaction
    e. G Is positive for all temperatures

    2. Relevant equations

    dG= dH - TdS

    3. The attempt at a solution

    The chemical reaction is going from liquid to gas, therefore the entropy is increasing because the reaction is causing more macrostates due to the greater area of distribution for the gas molecules. The reaction is exothermic, because its giving off heat.

    Therefore, Entropy is increasing (S is positive) and since no heat is being absorbed Enthalpy is decreasing (H is negative).

    So my answer is B.... so here's the dilemma,, B is the same answer as D. I don't know if this was a mistake on the teachers part, or I AM WRONG, and she put the answer there 2x to hint that its not the answer.
  2. jcsd
  3. Nov 9, 2009 #2


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    Science Advisor
    Homework Helper
    Gold Member

    Why do you say it's exothermic?
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