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Mia Navarro 1D
Posts: 52
Joined: Fri Sep 29, 2017 7:04 am


Postby Mia Navarro 1D » Sun Jan 28, 2018 5:04 pm

What equation do you use for the equation and why? What given values or key phrases in a word problem do you look for when determining to use this equation?

Jessica Jones 2B
Posts: 80
Joined: Fri Sep 29, 2017 7:04 am

Re: 9.19

Postby Jessica Jones 2B » Sun Jan 28, 2018 5:06 pm

I have similar question because you use the equation deltaS= Cp(ln(T2/T1), but I am confused as to if we are supposed to include the moles/grams in the equation or ignore them all together?

Anh Nguyen 2A
Posts: 36
Joined: Fri Sep 29, 2017 7:05 am
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Re: 9.19

Postby Anh Nguyen 2A » Sun Jan 28, 2018 9:31 pm

I think you have to first know what changes are happening in this process. There are 3 steps to this process:
1. Reversible heating of water liquid from 85 degree C to 100 degree C
For this you use the molar heat capacity at constant pressure of liquid water
2. Phase change from liquid to vapor
For this you use the standard entropy of vaporization at 100 degree C
3.Water vapor cools from 100 degree C to 85 degree C
For this you use the the molar heat capacity at constant pressure of water vapor

And yes, you have to include the moles in the equation because the numbers given are molar heat capacities and standard entropy whose units are J/K/mol so you have to multiply them with number of moles to get the entropy change. For this exercise, I just assume nH2O=1.00 mol.

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