Enthalpy of Combustion per mole of H2

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Discussion Overview

The discussion revolves around the relationship between the enthalpy of combustion per mole of hydrogen (H2) and the enthalpy of combustion per molar volume of hydrogen and methane (CH4). Participants explore the definitions and implications of "molar volume" and "per mole" in the context of enthalpy calculations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants question why the enthalpy of combustion for one molar volume is considered equivalent to that for one mole in this context.
  • One participant suggests that the enthalpy of combustion for one mole of H2 and CH4 can be expressed in terms of hypothetical values, leading to a comparison of ratios.
  • Another participant clarifies that "molar volume" refers to the volume occupied by one mole of gas at standard temperature and pressure (STP), implying a connection to the concept of "per mole."
  • There is a discussion about whether "molar" and "per mole" can be used interchangeably, with some participants asserting that they can in this case.
  • One participant expresses confusion over the use of both terms and seeks clarification on their equivalence.

Areas of Agreement / Disagreement

Participants exhibit both agreement and disagreement. While some agree that "molar volume" and "per mole" can be used interchangeably in this context, others express uncertainty about the implications of this equivalence and the definitions involved.

Contextual Notes

There are unresolved questions regarding the definitions of "molar volume" and "per mole," as well as the implications of using both terms in the discussion of enthalpy of combustion.

Integral0
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Enthalpyof Combustion of 1 molar volume of H2(g) divided by Enthalpyof Combustion of 1 molar volume of CH4(g)

=

Enthalpyof Combustion per mole of H2 divided by Enthalpy of Combustion per mole of CH4


why?
 
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Why does x/y = mx/(my)?
 
Re

I guess . . . I'm just writing down what the book says . . .
 
RE

I am asking why is one molar volume equal to one mole in this case at hand?
 


Originally posted by Integral0
I am asking why is one molar volume equal to one mole in this case at hand?
It isn't :)

Where does it say that the enthalpy of combustion for one mole or one molar is the same? The only thing the same, is the answer of the division, the fraction (by lack of a better word).
 
RE

why are the two expressions above (my first post) the same or equal?

My previous comment was wrong . . . I was just trying to piece together why they would be the same. "I am asking why is one molar volume equal to one mole in this case at hand?"
 
Please paraphrase your question --- the only thing that is clear is that you are struggling with a definition --- which definition it is, is not clear.
 
OK, let's look at it in the following way. Hypothetical numbers.


The enthalpy of burning 2 liter one molar H2 is x.
The enthalpy of burning 2 liter one molar CH4 is 2x.

So H2/CH4 would be x/2x.


Now, let's look at moles.

The enthalpy of burning one mole H2 is 0.5x
The enthalpy of burning one mole CH4 is x

So H2/CH4 would be 0.5x/x, which can rewritten as x/2x.



So x/2x = 0.5x/x.
 
RE

but the first expression says "Molar volume" while the second one says "per mole"?

Are they the same?

What is there relation to each other?
 
  • #10
Paraphrasing, "Does 'molar' mean 'per mole'?" In this instance, yes. "Molar volume" does mean volume per mole, and one molar volume is a way of saying one mole. Likewise, "molar enthalpy" is the same thing as saying enthalpy per mole.

For an instance in which "molar" does not imply one mole, consider 10 ml of a one "molar" solution --- "x molar" means x moles per liter of solution at whatever temperature is indicated for the glassware.
 
  • #11
Well, molar volume just means moles/liter, it is a concentration. While per mole is an absolute amount.

.. a few cogs have turned in my head .. maybe what is meant with a 1 molar volume, is the volume of gas that defines the amount of 1 mole??

hgm..
 
  • #12
RE

well, if "per mole" and molar volume can be used interchangeable in this situation, why did they use both?

I think we aren't understanding each other here.

I am asking in the question why can the two expressions equal each other since one specifies "Enthalpy of Combustion Per MOLE" and the other specifies "Enthalpy of Combustion of 1 molar volume".

Is the "Enthalpy of Combustion Per MOLE" the same as the "Enthalpy of Combustion of 1 molar volume"?

Molar volume is the volume occupied by one mole of ideal gas at STP. Its value is:

22.414 L mol¯1

Enthalpy of Combustion is the change of enthalpy in the standard state of formation per mole.

Any insights MONIQUE?
 
  • #13
AH! SEE! Good that you kept asking Integral0 :)

Here is the definition: The molar volume is the volume occupied by one mole of ideal gas at STP.

The unit is L mol^-1

So no matter what, you are always dealing with one mole, if you are talking about 1 molar volume, or per mole.
 
  • #14
awesome!

YOUR AWESOME MONIQUE!

PM me about biochemistry (your major concentration in college) . . .

Do you like it? etc . . . Experiences?
 
  • #15


hehe, sorry about talking past each other.. it is a strange example..

Originally posted by Integral0
well, if "per mole" and molar volume can be used interchangeable in this situation, why did they use both?
To illustrate that they can be used interchangeably?

Is the "Enthalpy of Combustion Per MOLE" the same as the "Enthalpy of Combustion of 1 molar volume"?
yes
 
  • #16


Originally posted by Integral0
YOUR AWESOME MONIQUE!
why, thanks. It had been a while that I had used the expression molar volume.. thanks for reminding me about it :wink:
 

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