Question

9. What effect does increase of the external pressure have on the boiling point of a liquid? 3 pts

Answer 1

Increasing external pressure will "pressurize" and "push" the volatile molecules to the liquid phase

Therefore, it is "harder" to vaporize

Expect the boiling point of a liquid to INCREASE as P is increased

we can prove this using Clasius equations:

Recall that in equilibrium; especially in vapor-liquid equilibriums, we can use Clasius Clapyeron combination equation in order to relate two points in the same equilibrium line.

The equation is given as:

ln(P2/P1) = -dHvap/R*(1/T2-1/T1)

Where

P2,P1 = vapor pressure at point 1 and 2

dH = Enthalpy of vaporization, typically reported in kJ/mol, but we need to use J/mol

R = 8.314 J/mol K

T1,T2 = Saturation temperature at point 1 and 2

Therefore, we need at least 4 variables in order to solve this.

Substitute all known data:

ln(P2/P1) = -dHvap/R*(1/T2-1/T1)

The slope is a negative, so the higher P, the higher T is required