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Entropy and enthalpy

  1. Nov 14, 2010 #1
    1. The problem statement, all variables and given/known data

    consider the decomposition of calcium carbonate: CaCO3(s) yields CaO(s) + CO2(g)

    a) calculate delta H and delta S from standard thermodynamic data.
    b) calculate delta G at 25.0C

    2. Relevant equations

    G = H - TS

    3. The attempt at a solution

    i added up all the thermodynamic data and got -2236 KJ/mol
    now this is the delta G but for (a) im not given a temperature(is it 25C) and i have to solve for two variables. not sure what to do.
  2. jcsd
  3. Nov 14, 2010 #2
    anybody please, can u at least get me started.
  4. Nov 16, 2010 #3
    1. list Hf values for CaCO3, CaO, CO2 (-1207,-635,-394 kJ/mole) (this is at 25C, 1 atm)
    2. H(reaction)=SUM(r*Hf), where r= reaction-coefficient= negative for reactants)
    3. similar for entropy.
    4. use G=H-TS for the calculation of G(reaction)
  5. Nov 16, 2010 #4
    Delta H and Delta S Values:
    (click Entropy and Enthalpy Tab)

    Use Products - Reactants with the values on the website above to determine the overall delta H and delta S.

    (Values for Products) - (Values for Reactants)

    Then, once you have delta S and delta H, you can use the formula you provided above to find delta G.

    You can also verify that your delta G is correct by using the values in the chart to see if you come out with the same answer. Make sure that you keep your values consistent! Entropy is often in J/mol while the others are in kJ/mol.
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