[XGen]

A liquid has a vapor pressure of 40 mmHg at 19.0 C and a normal boiling point of 78.3 C. What is its enthalpy of vaporization in kJ/mol?

In the beginning pages of this test is this formula:

ln K = (- :delta: H)(1/RT) + c

However, I am at a loss for what this means. I realize it is a manipulation of the formulas  :delta: G =  :delta: H - T :delta: S and  :delta: G = -RT ln K, but I do not know what the value of c is or its origin.

Any help would be appreciated!


Oh, and one more question:
Which forms the most alkaline solution when added to water?
A) Al₂O₃ B) B₂O₃ C) CO₂ D) SiO₂

I can immediately rule out carbon dioxide as it forms carbonic acid. Silicon dioxide is also known as quartz, and I know not of any significant reactions between water and it. I would assume that boron trioxide would form boric acid. However, isn't aluminum oxide insoluble in water? Would the negligible amount of solid dissolved be considered the most alkaline solution?

[PIQgoogleme]

First problem: read up on the Clausius-Clapeyron equation

lnP₂/P₁= -Delta H/R _vap (1/T₂ - 1/T₁)

-->

(R*lnP₂/P₁)/(1/T₁ - 1/T₂) = Delta H_vap

Second problem:
The more metallic the element, the more basic the oxide. Pretty sure it's as simple as that. C and D definitely don't work. Pretty sure B doesn't either. Maybe under really high temperatures Aluminum Oxide reacts with water?

[XGen]

Thanks for your reply! When I googled the formula, I couldn't find the name. Now I know it's called the Clausius-Clapeyron equation.