## Bond Enthalpy and Enthalpy of Formation

Brian Huynh 3D
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Joined: Wed Sep 21, 2016 2:58 pm

### Bond Enthalpy and Enthalpy of Formation

Professor Lavelle covered in class that the Enthalpy of formation of O2 is 0. Are there any other exceptions like this?

Maggie Bui 1H
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### Re: Bond Enthalpy and Enthalpy of Formation

It's not so much that O2 is an exception as it is that the standard enthalpy of formation of an element in its most stable form is 0 (this definition is found on page 294 of the book). I think this makes more sense if you think about the "reaction" you'd need to form these elements. You could write down a reaction, but since the reactants of the reaction would be the constituent elements in their most stable form, the reactants and products of a reaction making an element in its most stable form would be the same.

Celina N 2H
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### Re: Bond Enthalpy and Enthalpy of Formation

The enthalpy of formation of oxygen (O2) is 0 because O2 is the element oxygen in its most stable state. Therefore, elements in their most stable states (e.g., H2 for hydrogen, F2 for fluorine, C for carbon, etc.) all have enthalpy of formation equal to 0. In all other less stable forms, enthalpy of formation will not equal 0.

Jocelyn_Limas_2G
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### Re: Bond Enthalpy and Enthalpy of Formation

If the standard enthalpy of formation is not found on the tables given, is it then safe to assume that it equals 0?

Trisha Agarwal 1O
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Joined: Wed Sep 21, 2016 2:56 pm

### Re: Bond Enthalpy and Enthalpy of Formation

If it's not on the table it is most likely an element that is in its standard state, so I it would be 0.