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Homework Help: Enthalpy Questions

  1. Sep 21, 2011 #1
    1. The problem statement, all variables and given/known data

    1) Use the data tables provided in at the back of your textbook to calculate the phase transition heat for 1.0 g of liquid benzene (MW = 78.12 g mol-1) as it solidifies at its freezing point at standard pressure.

    1. 0.39 kJ mol-1
    2. -0.39 kJ mol-1
    3. 0.14 kJ mol-1
    4. -0.14 kJ mol-1
    5. There is not enough information provided to answer this question.

    2) True or False?

    If your body evaporates 1 L of sweat from your skin at 25oC then more than 2400 kJ of heat will have been removed from your body by this process. (Use the data at the back of the textbook and assume that the physical properties of sweat are identical to those of water.)

    3) True or False: According to Hess' Law, the overall enthalpy change in going from reactants to products does not depend on the series of reactions taken, even if some of the reactions were done at constant volume.

    2. Relevant equations

    3. The attempt at a solution

    I know that n = 1/78.12 = 0.0128 mol
    I know that "K"(freezing) for benzene = 5.12 K kg mol^-1
    I know that standard pressure = 1 bar = 10^5 Pa
    I also know that T = 273.15 K at the freezing point.
    As for formulas and such, I'm stuck because our teacher wants us to read ahead and I can't find ANYTHING! T__T

    V = 1 L = 1 m^3
    T = 298.15 K
    q = 2400 kJ
    (delta)H(vap)[H2O] = 40.7 kJ mol^-1

    3) I want to say false because the change does depend on the series of reactions taken (they each have their individual enthalpy).

    Thoughts? I'm really lost! =O
  2. jcsd
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