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Enthalpy of phase change

Posted: Thu Feb 07, 2019 3:08 pm
by Katie Frei 1L
In the example given in class, to calculate the net enthalpy change of the reaction of Br2(l) becoming 2Br(g), why is the change of enthalpy of vaporization added to the change of bond enthalpy?

Re: Enthalpy of phase change

Posted: Thu Feb 07, 2019 3:30 pm
by Chem_Mod
Because it has two components, one the energy required to break the bonds and the other is the energy required to vaporize the Br

Re: Enthalpy of phase change

Posted: Sat Feb 16, 2019 9:37 pm
by Cameron_Greenberg_3C
When a phase change occurs in the reaction, there is an additional enthalpy change that must be accounted for on top of the normal reaction enthalpy. The enthalpies of molecules are different in different states.

Re: Enthalpy of phase change

Posted: Tue Feb 19, 2019 11:57 am
by Matthew Choi 2H
There are two parts to the process in which Br2 becomes 2Br. One part is the breaking of the bond between Br2, and the second part is the vaporization of Br2 to a gas.

Re: Enthalpy of phase change

Posted: Tue Feb 19, 2019 11:59 am
by Danielle_Gallandt3I
If the Br2 to 2Br stayed in the same phase then you would not have to consider the vaporization of Br, but since there is a phase change, this must be considered on top of the bonds of the molecule being broken

Re: Enthalpy of phase change

Posted: Thu Mar 14, 2019 2:37 pm
by CHEM 14B Lover
Breaking Br2 into 2Br doesn't automatically make the 2Br a gas.