Effect of pressure on melting point.

[ExcessRed]

Is there a quantifiable value for a given substance that correlates to the degree by which pressure has an effect on the element or substance melting/boiling point?

Allow me to elaborate.

If the substance in question is known (silicon dioxide, for example), how could we calculate the modified melting/boiling points given n bars of atmospheric pressure? Bonus points if you can explain why some chemicals skip the liquid phase under certain pressure conditions.

 

[ExcessRed]

Solved the problem myself, but thought you guys might like to know the solution:

T2 = 1/((1/(T1))-Math.log(Pressure/1)*R / (Hv * 1000));

R = 8.314
Pr = Pressure you're solving for (in bars.)
Hv = Heat of vaporization for the substance in kJ/mol.
T1 = Boiling point at 1 bar of pressure.
T2 = the solution!

Edit: To clarify, Math.log() in this context refers to log base e (2.718...)

 

[SteamKing]

This equation may be OK for boiling point change. But is it applicable to change in the melting point with change in pressure?

 

[Borek]

Any phase transition, but you need to use enthalpy value for that particular transition.

http://en.wikipedia.org/wiki/Clausius–Clapeyron_relation

 

[ExcessRed]

Are you sure it works with enthalpy of fusion? I've tried substituting the values for that phase change, but none of them are coming up correct.

 

[Borek]

Are you sure it works with enthalpy of fusion? I've tried substituting the values for that phase change, but none of them are coming up correct.

There are no assumptions about what kind phase transition takes place, however, there is an assumption that enthalpy is constant (not a function of P, T) - it is quite possible that's why you get incorrect result.