Standard Enthalphy of a reaction

Moderators: Chem_Mod, Chem_Admin

Miriam Velez 1I
Posts: 22
Joined: Fri Sep 25, 2015 3:00 am

Standard Enthalphy of a reaction

Postby Miriam Velez 1I » Fri Jan 08, 2016 10:49 pm

In the course reader, there is an example about standard enthalphy of combustion of methane. The problem says to "make sure everything is in standard state..." but I am a little bit confused by this statement. What if the compounds weren't in standard state? How do we convert the enthalphy we are given to standard state?

Brandon Truong 2G
Posts: 29
Joined: Fri Sep 25, 2015 3:00 am

Re: Standard Enthalphy of a reaction

Postby Brandon Truong 2G » Fri Jan 08, 2016 11:13 pm

In lecture, he said that if the compounds were not in standard state then we were suppose to treat it as if the compounds were in standard state and then adjust for the phase changes. I'm not sure how to do this but I think it involves taking difference between the amount of energy in the compounds not in standard state and the amount of energy in the compounds in standard state. Maybe he'll talk about it more in lecture on Monday.

VivianYang2A
Posts: 8
Joined: Fri Sep 25, 2015 3:00 am

Re: Standard Enthalphy of a reaction

Postby VivianYang2A » Fri Jan 08, 2016 11:36 pm

I think they would give us information to replace what is given with "standard state".

Chem_Mod
Posts: 18400
Joined: Thu Aug 04, 2011 1:53 pm
Has upvoted: 435 times

Re: Standard Enthalphy of a reaction

Postby Chem_Mod » Fri Jan 08, 2016 11:41 pm

Using the method of "products minus reactants" looking up values in the Appendix will give the standard enthalpy of reaction at 1 atm and 298 K. If some component of the reaction is not in standard state, you can always adjust for it by adding some other reactions via Hess's Law. You will soon encounter several of these types of homework problems (for example, find the enthalpy of combustion of methane at 400 K which is not standard temperature!) and it will also be explained further in lecture.


Return to “Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)”

Who is online

Users browsing this forum: No registered users and 0 guests