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[ellieee]

Homework Statement

I searched google and got very varied responses so I'm really confused.
I saw that boiling point will increase because: more energy is required for the solvent's vapor pressure to reach the external pressure.
however, I think it will decrease because:
when less pressure exerts on the liquid, less heat is needed to overcome the intermolecular forces of attraction and it can vaporize into a gas at a lower temperature.
and consequently, will freezing point increase or decrease when pressure decreases?
for this, I have the same thoery as for the boiling point

Relevant Equations

nil

nil

 

[anuttarasammyak]

and consequently, will freezing point increase or decrease when pressure decreases?
for this, I have the same theory as for the boiling point

You seem to assume both freezing point and boiling point go down with decreasing pressure. What kind of counterexamples have you found in the web ?

 

[ellieee]

You seem to assume both freezing point and boiling point go down with decreasing pressure. What kind of counterexamples have you found in the web ?

counterexample for boiling point:
I saw that boiling point will increase because: more energy is required for the solvent's vapor pressure to reach the external pressure.
counterexample for freezing point:
Because of increasing the pressure, which prevents water molecules properly arranging them. If water freezes, the mean forms a crystalline solid phase with a proper arrangement. ... That means water freezes at below 273K.

 

[anuttarasammyak]

Gas has larger volume than liquid. Pressure prevents tendency of materials to have larger volume. higher the pressure is, higher the boiling point is.

Liquid does not always have larger volume than solid, e.g. for water the higher the pressure is, the lower the freezing point. higher or lower according to pressure increase depends on this volume change property or bonding mechanism of each kind of material.

 

[Chestermiller]

The equilibrium vapor pressure of a fluid increases with increasing temperature. For a liquid to boil, bubbles of pure vapor must form within the bulk of the liquid (below the surface) to push the liquid out of the way. Subjecting the liquid to a higher pressure requires higher vapor pressure for the bubbles to form and push liquid out of the way. This higher vapor pressure requires a higher temperature.

 

[Lnewqban]

It is difficult to boil an egg at the peak of a very high mountain.
The water can never reach 100 degrees Celsius.