Vaporization of water below 100C?

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Payton Kammerer 2B
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Joined: Tue May 01, 2018 3:00 am

Vaporization of water below 100C?

Postby Payton Kammerer 2B » Sun Feb 09, 2020 11:20 pm

"Calculate the standard entropy of the vaporization of water at 85 degrees C, given that its standard entropy of vaporization at 100 degrees C is 109.0 J/K/mol and the molar heat capacities at constant pressure of liquid water and water vapor are 75.3 J/K/mol and 33.6 J/K/mol, respectively, in this range."

1) Why is the heat capacity of water vapor included? Isn't it irrelevant?
2) I am a little bit confused about the water being vaporized at 85 degrees. Should I be thinking about the atmospheric pressure as being different in order for the vaporization to occur, and adjusting the standard entropy at 100 degrees based off of that? Am I overthinking this?

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Re: Vaporization of water below 100C?

Postby Chem_Mod » Mon Feb 10, 2020 4:30 pm

Calculate the entropy change with the temp change from 85 - 100 C, then add the entropy of vaporization, then add the entropy of cooling the water vapor from 100 - 85 C. Thus you need the heat capacity of water to find entropy of the temperature changes. And yes, at different pressures you can get water to vaporize at a lower temperature.


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