Standard Conditions and Molar Enthelpy Changes

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Discussion Overview

The discussion revolves around the concept of standard conditions in relation to various molar enthalpy changes, including atomization enthalpy, formation enthalpy, combustion enthalpy, and others. Participants explore whether it is meaningful to define these quantities under standard conditions and the implications of such definitions.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Homework-related

Main Points Raised

  • Some participants suggest that standard conditions are applicable to all listed quantities except for atomization enthalpy, ionization energy, electron affinity, and bond energy.
  • Others express uncertainty about how to extrapolate molar enthalpy values to standard conditions.
  • It is proposed that for enthalpies to be comparable, they must be extrapolated to either standard or identical conditions, with Hess's law mentioned as a method for this.
  • One participant questions whether the concept of "comparability" adequately addresses the original question about standard conditions.
  • There is a discussion about the potential differences in ionization energy at varying temperatures and pressures, with some suggesting that at low enough temperatures, differences may not occur.
  • Concerns are raised about the practical challenges of measuring ionization energies of non-volatile elements at low temperatures.
  • A later reply posits that all the quantities discussed may depend on temperature and pressure to varying extents, although the extent of this dependence is not fully agreed upon.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the applicability of standard conditions to the various quantities discussed. Multiple competing views remain regarding the definitions and implications of standard conditions in relation to molar enthalpy changes.

Contextual Notes

Participants express uncertainty about the extrapolation of molar enthalpy values and the conditions under which these values are measured, indicating that assumptions about temperature and pressure may affect the discussion.

PFuser1232
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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?
 
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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?
 
Borek said:
This is a pretty good homework question if you ask me. Moving it.

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

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?
 
Borek said:
This is a pretty good homework question if you ask me. Moving it.

Whether it is HW or not - what are your thoughts?
MohammedRady97 said:
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?

?
 
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.
 
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Borek said:
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.

What about the first question?
 
Doesn't "comparability" answer it?

Really, a lot depends on what you are aiming at, so the answer is "it depends".
 
Borek said:
Doesn't "comparability" answer it?

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

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

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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