why is H negative when calculating S?


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aisteles1G
Posts: 117
Joined: Fri Sep 28, 2018 12:15 am

why is H negative when calculating S?

Postby aisteles1G » Sun Feb 10, 2019 12:25 pm

This question in the 7th ed is 4F.13: Use data in Table 4C.1 or Appendix 2A to calculate the entropy change for (a) the freezing of 1.00 mol H 2 O (l ) at 0.00

I did it correctly but my answer was positive not negative; for H(fus) the book uses -6.01 when solving for S(fus) and I thought we could just use +6.01, so I'm confused as to why it's negative?

Jenna Salas 2H
Posts: 30
Joined: Fri Sep 28, 2018 12:22 am

Re: why is H negative when calculating S?

Postby Jenna Salas 2H » Sun Feb 10, 2019 2:46 pm

It's negative because you are going from a liquid to a solid. DeltaH of fusion is positive when you go from a solid to a liquid.

Rami_Z_AbuQubo_2K
Posts: 89
Joined: Thu Jun 07, 2018 3:00 am

Re: why is H negative when calculating S?

Postby Rami_Z_AbuQubo_2K » Sun Feb 10, 2019 4:48 pm

It is because fusion is the opposite of freezing.

Katelyn Phan 2A
Posts: 61
Joined: Fri Sep 28, 2018 12:23 am

Re: why is H negative when calculating S?

Postby Katelyn Phan 2A » Mon Feb 11, 2019 9:16 am

Freezing is an exothermic process, thus the transfer of energy is released.

Melissa Bu 1B
Posts: 36
Joined: Fri Sep 28, 2018 12:19 am

Re: why is H negative when calculating S?

Postby Melissa Bu 1B » Mon Feb 11, 2019 9:42 am

When you go from a liquid to a solid, delta S is negative because the molecules are more ordered (less disordered).


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