Increasing pressure does what to temperature?

[ebunny91]

Homework Statement

A certain substance exists in two phases at equilibrium at Temp T1 and pressure P1. One phase α is a crystalline solid (density 0.531 g/cm^3) while the other phase β is an amorphous glass (density 0.510 g/cm^3).

a) If the external pressure is increased, will the temp at which the α→β conversion takes place increase or decrease?

b) If the external pressure is increased isothermally, what will happen?

Homework Equations

density=mass/volume

dP/dT = ΔHvap/TΔV ??

The Attempt at a Solution

a) If the external pressure is increased, will the temp at which the α→β conversion takes place increase or decrease?

I know that the curve between the two phases is where the two phases exist at equilibrium and that it is dP/dT and that relates to density (which is 1/V).

I want to say that if you increase the pressure, the temp of the conversion will increase but I am assuming that the curve looks like that of a water phase diagram. How do I determine if it increases or decreases by using the density?

b) If the external pressure is increased isothermally, what will happen?

Increasing pressure isothermally means that the temperature stays constant. So we will end up with only one phase (I'm not sure which, the α or the β. I feel like this might also have something to do with the density.)

 

[Borek]

IMHO For the first part LeChatelier's principle is enough. When pressure goes up, system tries to occupy lower density, so the higher density phase becomes favored. Now just try to apply this line of thinking to the question.