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Standard Conditions and Molar Enthalpy Changes

  1. Oct 20, 2014 #1
    The following is a list of various quantities (molar enthalpy changes) found in a typical Chemistry course:

    • Atomization Enthalpy
    • Formation Enthalpy
    • Combustion Enthalpy
    • Neutralization Enthalpy
    • Solution Enthalpy
    • Hydration Enthalpy
    • Ionization Energy
    • Electron Affinity
    • Lattice Energy
    • Bond Energy (and mean bond energy)
    • Lattice Dissociation Enthalpy
    • Reaction Enthalpy
    For which of the aforementioned quantities is it meaningful to include "standard conditions" as a part of the quantity's definition?
     
  2. jcsd
  3. Oct 21, 2014 #2

    Borek

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    This is a pretty good homework question if you ask me. Moving it.

    Whether it is HW or not - what are your thoughts?
     
  4. Oct 21, 2014 #3
    It's not homework actually.
    Well, I think standard conditions are applicable to all of the above quantities except atomization enthalpy, ionization energy, electron affinity, and bond energy. Is that correct? Frankly, I still have trouble imagining how we can extrapolate other molar enthalpy values to standard conditions. Anyway, is my answer correct?
     
  5. Oct 22, 2014 #4
    ?
     
  6. Oct 22, 2014 #5

    Borek

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    In general, if we want enthalpies of a process to be comparable, we have to somehow extrapolate them - if not to standard, then at least to identical conditions.

    You can always use Hess law for that.
     
  7. Oct 22, 2014 #6
    What about the first question?
     
  8. Oct 22, 2014 #7

    Borek

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    Doesn't "comparability" answer it?

    Really, a lot depends on what you are aiming at, so the answer is "it depends".
     
  9. Oct 22, 2014 #8
    So, for instance, would ionization energy at 298 K and 101 kPa differ from ionization energy at some other pressure and temperature?
     
  10. Oct 22, 2014 #9

    Borek

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    As far as I can tell, as long as the temperature is low enough for the molecules to be in the ground state - it shouldn't.

    But I am not convinced measuring ionization energies of non-volatile elements can be done at low temperatures, so it can be a practical problem.
     
  11. Oct 22, 2014 #10
    So is it correct to say that all of the quantities above depend on temperature and pressure to varying extents (however small)?
     
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