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Phase change?

by doomed
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doomed
#1
Oct9-05, 04:30 PM
P: 1
How do I calculate the values of change in entropy (S) and change in Gibbs free enery (G) for the conversion of n=1 mol of liquid water at 100 C and 1 bar pressure in to vapor at the same temperatue and a pressure of 0.1 bar. Assume ideal behavior for the vapor. the molar enthalpy for vaporization of water at 100 C and 1 bar is 40.6 kJ/mol.

I know that delta S = delta H/T, but how the change in pressure play into this problem for delta S and delta G????

HELP me PLEASE!
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clive
#2
Oct9-05, 05:49 PM
P: 120
I'll give you some hints for the entropy:

You have 2 thermodynamic processes there:
1) vaporization
2) isothermal expansion form 1 bar to 0.1 bar.

Because the temperature is the same, the variation in entropy can easily be evaluated by
[tex]\Delta S=\frac{Q_1+Q_2}{T}[/tex]
where Q1+Q2 represents the total transfered heat.

Now you have
[tex]Q_1=m\cdot \lambda_v[/tex]
for the vaporization at 100 C
and
[tex]Q_2=\nu R T \ln \frac{V_2}{V_1}[/tex]
for the isothermal expansion

and so on.......([tex]p_1 V_1=p_2 V_2[/tex] is the answer at your last question)
Tom Mattson
#3
Oct9-05, 06:33 PM
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doomed,

1.) Post only one thread per topic.

2.) Post homework questions in the Homework Help Forums, not the Physics Forum.


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