van der waals constants

[rthmjohn]

I had a little debate with my teacher over this test question:

 

One of the van der waals constants, a or b, can be correlated with the boiling point of a substance. Specify which constant and how it is related to the boiling point.

 

Any comments? I thought it was b (atomic/molecular size), but apparently I was wrong...

[The Thing]

Lol what a coincidence. I JUST finished the article in WiSci about van der Waals equation about 20 seconds ago.

Boiling point of a liquid can be defined as the temperature at which the vapor pressure of the liquid equals the outside pressure upon the liquid.

It also means the boiling point is a temperature at which the liquid has enough energy to break free of the forces of attraction between its molecules.

In the article I mentioned this, so I'll mention it again. One of the things the ideal gas law missed was the forces of attraction, without which a gas cannot ever become a liquid. So it is because of these forces of attraction (with which a is connected) that the gas can change phases.

So knowing theses, you can see why there's a relationship between a and the liquid's boiling point, because the stronger the forces of attraction within the liquid, the higher the boiling point would be.

[Cap'n Refsmmat]

The article mentioned, with the suitable maths included

[rthmjohn]

awesome. thanks