# Homework Help: Leidenfrost effect at thermodynamic equilibrium

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1. Mar 24, 2017

### digogalvao

1. The problem statement, all variables and given/known data
A spherical drop of a pure substance floats on top of the vapor of the same substance so the system vapor+drop is isolated. The drop has a surface tension σ. Show that at the thermodynamic equilibrium PL≠PV and calculate the difference.

2. Relevant equations
Three laws of thermodynamics

3. The attempt at a solution
I solved this one already but I would like to check my result. Following the three laws of thermodynamics and maximizing the entropy at the equilibrium yadda yadda yadda I got PL-PV=3σ/a, where a is the radius of the drop. The dimension of the result seems correct.

2. Mar 24, 2017

### kuruman

Is there a question here? If the question is "Am I right?", you have to supply the "yadda, yadda, yadda" so that someone can check your work and point out possible mistakes.

3. Mar 24, 2017

### digogalvao

Ok...
For σ=0, Thermodynamic equilibrium says: PL=PV, but if we add a work therm for the liquid -σdS=-3σdV/a we get PL-PV=3σ/a.