# Homework Help: First order phase transition (van der waals gas)

1. Apr 19, 2010

### jasony

1. The problem statement, all variables and given/known data
Give the physical explanation of the graphs (Fig 4(a) and 4(b)) on Page 4
http://www.pma.caltech.edu/~mcc/Ph127/b/Lecture3.pdf" [Broken]

2. Relevant equations

1) Why $$V_{g}$$ decreases with temperature but $$V_{l}$$ increases with temperature
2) Why must phase transition happen at constant pressure (Maxwell construction)

3. The attempt at a solution

4(a) As temperature increases, greater proportion of molecules acquire sufficient energy to escape from liquid and consequently a higher pressure is needed to establish equilibrium between liquid and vapour

4(b) don't really know how to explain
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

Last edited by a moderator: May 4, 2017
2. Apr 22, 2010