# Homework Help: Standard Conditions and Molar Enthalpy Changes

1. Oct 20, 2014

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. Oct 21, 2014

### Staff: Mentor

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

Whether it is HW or not - what are your thoughts?

3. Oct 21, 2014

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?

4. Oct 22, 2014

?

5. Oct 22, 2014

### Staff: Mentor

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.

6. Oct 22, 2014

7. Oct 22, 2014

### Staff: Mentor

Really, a lot depends on what you are aiming at, so the answer is "it depends".

8. Oct 22, 2014

So, for instance, would ionization energy at 298 K and 101 kPa differ from ionization energy at some other pressure and temperature?

9. Oct 22, 2014

### Staff: Mentor

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.

10. Oct 22, 2014