Bond enthalpies and phase changes

[Valerie Doan 3I]

Using the bond enthalpy method, how do we find the net enthalpy change for a compound that undergoes a phase change? For example, in lecture Dr. Lavelle used the example Br2 (l) --> Br2 (g) --> 2Br (g).

[jessicaosuna_1F]

I think you use bond enthalpy from the table and just add that to the enthalpy of the phase change which I assume would be given as well...

[605291562]

I agree with above that you use the table and add that to the enthalpy of the phase change which I assume would be given, if not does anyone know how to calculate that?

[Lorena_Morales_1K]

can someone explain the significance of phase changes?

[Lorena_Morales_1K]

whats the connection between enthalpy and Hess's law?

[Sera Aintablian 2E]

whats the connection between enthalpy and Hess's law?

For questions regarding Hess's Law, you can be given the enthalpies of the reactions (which you later manipulate while working on these types of problems), which you can use, because enthalpy is a state function.

[Elizabeth Kaplan 3I]

Hi! I think you are just to supposed to determine which bonds are broken in the reactants and which bonds are formed in the products, and then add the enthalpy values of those bonds together (make sure the enthalpy values for the bonds broken are positive because it requires energy, and that the enthalpy values for the bonds formed are negative because it releases energy).