Units of Reaction Enthalpies
Moderators: Chem_Mod, Chem_Admin
-
- Posts: 33
- Joined: Wed Sep 21, 2016 3:00 pm
- Been upvoted: 2 times
Units of Reaction Enthalpies
When we calculate reaction enthalpies for reaction that have more than one product or the balanced reaction has multiple moles of a product; what unit should we use?
Should we write kJ/mol or just kJ (since there are multiple moles)?
Should we write kJ/mol or just kJ (since there are multiple moles)?
-
- Posts: 23
- Joined: Fri Jul 15, 2016 3:00 am
-
- Posts: 33
- Joined: Wed Sep 21, 2016 3:00 pm
- Been upvoted: 2 times
Re: Units of Reaction Enthalpies
But what if the product generated is not one mole in quantity?
Or if there are multiple products? (so multiple moles of each)
Or if there are multiple products? (so multiple moles of each)
-
- Posts: 23858
- Joined: Thu Aug 04, 2011 1:53 pm
- Has upvoted: 1253 times
Re: Units of Reaction Enthalpies
I will answer this in detail in all my classes today, Friday.
Reaction enthalpy is often kJ.
There are times when it is kJ.mol-1.
If someone wants to post a summary here of what I discuss in class that would be great.
Also see examples I already covered in class. If someone wants to quote examples (page numbers) from lecture notes for others to see when I used kJ and kJ.mol-1 that would also be a helpful summary.
Reaction enthalpy is often kJ.
There are times when it is kJ.mol-1.
If someone wants to post a summary here of what I discuss in class that would be great.
Also see examples I already covered in class. If someone wants to quote examples (page numbers) from lecture notes for others to see when I used kJ and kJ.mol-1 that would also be a helpful summary.
-
- Posts: 21
- Joined: Wed Sep 21, 2016 2:57 pm
Re: Units of Reaction Enthalpies
When the question specifies, that it is per mole you would use KJ/mol. Also in addition to that by definition the standard enthalpy of formation is KJ/mol.
-
- Posts: 23858
- Joined: Thu Aug 04, 2011 1:53 pm
- Has upvoted: 1253 times
Re: Units of Reaction Enthalpies
Jasleen Kaur 1J wrote:When the question specifies, that it is per mole you would use KJ/mol. Also in addition to that by definition the standard enthalpy of formation is KJ/mol.
Yes and yes.
-
- Posts: 22
- Joined: Wed Sep 21, 2016 2:57 pm
Re: Units of Reaction Enthalpies
The units used are dependent on the situation. Typically, it is given in kj/mol unless otherwise stated.
-
- Posts: 15
- Joined: Wed Sep 21, 2016 2:59 pm
Re: Units of Reaction Enthalpies
Only for standard enthalpy of formation is it uniform to use kj/mol but if the also depends on what the question specifies. Its usually kj though
-
- Posts: 16
- Joined: Wed Sep 21, 2016 2:59 pm
Re: Units of Reaction Enthalpies
It can be either kJ/mol or kJ, just keep in mind the coeffecients of the products and what the question wants you to give as a final answer.
-
- Posts: 33
- Joined: Wed Sep 21, 2016 2:56 pm
Re: Units of Reaction Enthalpies
To give an example,
we used kj/mol for the standard enthalpy of formation of ethanol for the example (page 17 of the course reader) because the definition of the standard enthalpy of formation has to do with 1 mol of the product that was formed from the reactants. The same goes for the second example on page 18.
On page 16, we used kJ for the total enthalpy change because each reaction has a deltaH. The kJ in this case is not in context of moles, but of the reaction, and we use the kJ for each reaction to find the total enthalpy change in kJ.
we used kj/mol for the standard enthalpy of formation of ethanol for the example (page 17 of the course reader) because the definition of the standard enthalpy of formation has to do with 1 mol of the product that was formed from the reactants. The same goes for the second example on page 18.
On page 16, we used kJ for the total enthalpy change because each reaction has a deltaH. The kJ in this case is not in context of moles, but of the reaction, and we use the kJ for each reaction to find the total enthalpy change in kJ.
-
- Posts: 11
- Joined: Wed Sep 21, 2016 2:55 pm
Re: Units of Reaction Enthalpies
In last Friday's lecture by Dr. Lavelle, it was stated that the units of reaction enthalpies depends strictly on what is being asked. For example, if the question asks for the enthalpy of a formation reaction for a single molecule, it would be kJ/mol. If it does not happen like this, it will simply be kJ.
-
- Posts: 22
- Joined: Wed Sep 21, 2016 2:57 pm
Re: Units of Reaction Enthalpies
So basically to summarize:
q is generally in kJ
Delta H usually in kJ
Standard enthalpy of formation is only kJ/mol
q is generally in kJ
Delta H usually in kJ
Standard enthalpy of formation is only kJ/mol
Who is online
Users browsing this forum: No registered users and 15 guests