Register to reply

Phase change?

by doomed
Tags: phase
Share this thread:
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????

Phys.Org News Partner Science news on
Scientists discover RNA modifications in some unexpected places
Scientists discover tropical tree microbiome in Panama
'Squid skin' metamaterials project yields vivid color display
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
[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
Oct9-05, 06:33 PM
Sci Advisor
PF Gold
Tom Mattson's Avatar
P: 5,532

1.) Post only one thread per topic.

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

Register to reply

Related Discussions
Phase change Introductory Physics Homework 7
Phase Change Prob Biology, Chemistry & Other Homework 0
Phase Change: What is actually going on? General Physics 2
Phase change question Introductory Physics Homework 2
Phase Change Help General Physics 1