Reaction Enthalpy v. Enthalpy of Formation

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Caroline C 1G
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Joined: Fri Sep 29, 2017 7:05 am

Reaction Enthalpy v. Enthalpy of Formation

Postby Caroline C 1G » Thu Jan 18, 2018 8:16 pm

How do you know when to use reaction enthalpy instead of enthalpy of formation and vice versa?

Lucian1F
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Re: Reaction Enthalpy v. Enthalpy of Formation

Postby Lucian1F » Thu Jan 18, 2018 9:36 pm

It will probably be stated in the question and only one of these will probably be given to you to solve a problem. If both are given, you may need to combine the two methods or choose to do either method if the problem can be solved like that

Michael Lee 2I
Posts: 51
Joined: Fri Sep 29, 2017 7:05 am

Re: Reaction Enthalpy v. Enthalpy of Formation

Postby Michael Lee 2I » Thu Jan 18, 2018 10:11 pm

Usually the problem states whether it involves Reaction Enthalpy or Enthalpy of Formation. Sometimes both are needed if given the information.

Wayland Leung
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Re: Reaction Enthalpy v. Enthalpy of Formation

Postby Wayland Leung » Thu Jan 18, 2018 10:48 pm

What is the difference between the two?

nathansalce 3e
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Joined: Thu Jul 27, 2017 3:01 am

Re: Reaction Enthalpy v. Enthalpy of Formation

Postby nathansalce 3e » Fri Jan 19, 2018 11:10 pm

The difference between reaction enthalpy and enthalpy of formation relies on the info given. Reaction enthalpy would require the use of Hess's Law, but in order to execute Hess's Law, you must know/ be given the total change in enthalpy a specific reaction produces. Typically this is given to you in a chart, or next to the problem where you can then use Hess's law. Enthalpy of formation requires info on the specific formation of an individual molecule, for example N2 or CO2. Typically, molecules exothermically change in enthalpy in order to form the molecule, providing you the information necessary to add up all the specific formations of each molecule in the reactants and products. However, it is worth noting that molecules like N2 do not have formation enthalpies because in nature, N2 occurs naturally where as N does not occur alone.


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