Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Enthalpy = internal energy+pressure*volume

  1. Apr 17, 2005 #1
    My chem book says that

    Enthalpy = internal energy+pressure*volume

    However it says that enthalpy for a particular state cannot be calculated. Only the enthalpy change can be calculated. This has me confused.
    Aren't internal energy, pressure and volume calculabe for a particular state? Then why can't we calculate absolute enthalpy?
  2. jcsd
  3. Apr 17, 2005 #2
    Enthaply is used to calculate how much energy is taken in or released by a reaction where bonds have been broken (well all reactions really need bonds to brake but still...).

    Enthaply, however, also depends on the temperature (if I am correct) and ,thus, it is only possible to have an equation for the change.

    This might help or checking the rest of these might as well.

    The Bob (2004 ©)
  4. Apr 17, 2005 #3


    User Avatar
    Science Advisor
    Homework Helper

    It should be change in PV, or [tex] \Delta PV[/tex], the work in expansion against the atmosphere
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook