8.67(a)- how do we know the phase?

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sofiakavanaugh
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8.67(a)- how do we know the phase?

Postby sofiakavanaugh » Mon Jan 22, 2018 1:00 pm

In 8.67 part a, it asks you to calculate the enthalpy of formation in the liquid state of water. I get that we need to use the equation H2 + 1/2O2--> H20 (l) for this using the bond enthalpies. What I don't understand is why in the solutions manual it says that when we calculate the enthalpy for this rxn using the bond enthalpies that that value is actually for water in the gas phase not in the liquid phase. How do we know that? Is this something we need to memorize? How would we be able to distinguish between what phase other substances are in besides water?

Thanks!

Chem_Mod
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Re: 8.67(a)- how do we know the phase?

Postby Chem_Mod » Mon Jan 22, 2018 2:21 pm

The phase is not something you will be required to memorize. However, it is important to know when to use the appropriate equation such that you account for whether an element is going from solid to liquid, liquid to gas, etc.

Hope this helps!

Gurkriti Ahluwalia 1K
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Joined: Fri Sep 29, 2017 7:07 am

Re: 8.67(a)- how do we know the phase?

Postby Gurkriti Ahluwalia 1K » Mon Jan 22, 2018 10:49 pm

in part c of this problem, why is it not acceptable to do 6 mol of C-C bonds? in other words, what does 3 mol CRC bonds mean, and why is this seprate from 3 mol C-C?


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