phase change?????

by doomed
Tags: phase
 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!
 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 $$\Delta S=\frac{Q_1+Q_2}{T}$$ where Q1+Q2 represents the total transfered heat. Now you have $$Q_1=m\cdot \lambda_v$$ for the vaporization at 100 C and $$Q_2=\nu R T \ln \frac{V_2}{V_1}$$ for the isothermal expansion and so on.......($$p_1 V_1=p_2 V_2$$ is the answer at your last question)
 Emeritus Sci Advisor PF Gold P: 5,540 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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