1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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?
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook