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Expansion Work

  1. Sep 27, 2009 #1
    Expansion Work -- Still confused.

    This is more of a general question regarding thermodynamics. If you have a combustion reaction, and it produces either liquid water or water vapor--which case results in higher expansion work? My enthalpy calculations show higher PV work for the reaction with liquid water as the product, but intuitively, I feel like the reaction producing water vapor would do more work because a greater amount of gas is produced.

    Thanks in advance for your input!
     
    Last edited: Sep 27, 2009
  2. jcsd
  3. Sep 27, 2009 #2
    I guess I should specify. The way I calculated the enthalpy of combustion was by subtracting the enthalpies of formation for the reactants from those of the products--a generic way to get the enthalpy change for any reaction. However, since water (gas) has a higher Hf, the overall H of the combustion is also higher (less negative value). This suggests that the combustion of a compound to CO2 and H2O (g) actually releases less energy (i.e., less work can be done).

    Please give me your input... Am I not justifying this correctly?
     
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