Stuck on Question 8.67  [ENDORSED]

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Chiao-Wei Cheng 3e
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Stuck on Question 8.67

Postby Chiao-Wei Cheng 3e » Sat Jan 21, 2017 7:00 pm

The question is Use the information in Tables 8.3, 8.6, and 8.7 to estimate the enthalpy of formation of each of the following compounds in
the liquid state. The standard enthalpy of sublimation of carbon is -717 kJ/mol.
(a) H 2 O; (b) methanol, CH 3 OH; (c) benzene,C 6 H 6 (without resonance); (d) benzene, C 6 H 6 (with resonance).
I have no idea how to start this problem.
For (a), do I first write out an equation for the formation of H2O, add the bond enthalpies of H-H and half of O-O and subtract the 2 bond enthalpies of the O-H bond? What else would I need to do?

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Joined: Wed Sep 21, 2016 2:58 pm

Re: Stuck on Question 8.67  [ENDORSED]

Postby Tiffany_Luu_1F » Sat Jan 21, 2017 8:34 pm

Yes, that is what I did but then I also had to subtract by the heat of vaporization of H2O because it is asking for the liquid state. So once you do the [bonds broken] - [bonds formed] you get -242 kj/mol, and then you subtract this by 40.7 to get -282.7 kj/mol

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