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Homework Help: Equilibrium of stearic acid dimerization when dissolved in hexane

  1. Feb 24, 2008 #1
    1. The problem statement, all variables and given/known data

    Stearic acid, nature's most common fatty acid, dimerizes when dissolved in hexane:
    2C17H35COOH --> (C17H35COOH)2 H°rxn = -172 kJ
    The equilibrium constant for this reaction at 28°C is 2900. Estimate the equilibrium constant at 38°C.

    1) 4.7 *10^5
    2) 1.9 * 10^3
    3) 2.6 *10^4
    4) 18
    5) 3.2 *10^2

    3. The attempt at a solution

    The reaction is exothermic( since delta H is negative)
    therefore the actual equation will look like:

    2C17H35COOH --> (C17H35COOH)2 + heat

    If the temperature chanages from 28C to 38C it means that
    the heat is added to the system, thus, the equilibrium will shift towards left.
    this will cause the reactant to increase
    making Kc to decrease. (since Kc= product/reactant)

    So I eliminated answer choices that are larger than 2900 (the Kc at 28C).
    And I'm left with 2, 4, and 5.
    The anwer choice 2 seems to be the most reasonable
    since it decrease by 100, and the other answers seem to decrease too much.
    But I'm not positive about my decision.
    Is there any way to actually caculate Kc value, or is my method correct?

    Last edited: Feb 24, 2008
  2. jcsd
  3. Feb 25, 2008 #2
    Does anyone know how to slove this question?????
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