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9.15

Posted: Sat Feb 10, 2018 8:06 pm
by Sarah Rutzick 1L
For 9.15 part a, the answer book gives the heat of fusion as -6.01 kJ/mol. How do we know that the heat of fusion should be negative?

Re: 9.15

Posted: Sat Feb 10, 2018 8:36 pm
by Ammar Amjad 1L
The book gives the heat of fusion of water as 6.01 kj.mol^-1, meaning thats how much energy is required to go from solid to liquid water. However, the question is asking you to calculate the entropy for the freezing of water; therefore, you would use negative heat of fusion, because that's how much energy the system will release.

Re: 9.15

Posted: Sat Feb 10, 2018 9:26 pm
by Rachel Formaker 1E
Heat is always required to melt a substance, so ∆H is positive.

Heat is released when a substance freezes, so ∆H is negative.

∆Hfreezing = ∆Hfusion, and since you are given ∆Hfusion from Table 8.3, you just reverse the sign of ∆Hfusion to get ∆Hfreezing = -6.01 kJ/mol

Re: 9.15

Posted: Sun Feb 11, 2018 2:36 pm
by Manvir2K
How do you get -6.01 kJ/mol or 4.35 kJ/mol from appendix 2A?