how does????

Question

the vapour pressures of a liqiud depend on the intermolecular forces??????

Answer 1

The vapor pressure very nicely related to the intermolecular forces between the molecules. If the intermolecular forces are very strong, then the molecules of the liquid can't escape easily (they'll need much more energy to leave) and so the vapor pressure is rather low. If the intermolecular forces are very weak, the molecules can easily escape from the liquid, and so the vapor pressure is relatively high.

Answer 2

If molecules attract one another, then the liquid will have a lower vapor pressure than if they do not or attract one another less. One way to look at the problem is with boiling points. This is because the boiling point is the temperature at which the vapor pressure equals the atmospheric pressure. So compounds with higher vapor pressures get there "first."

The boiling point of H2O is 100C and of CCl4 77C. Yet the molecular weight of water is 18 and of CCl4 154. This is because H2O molecules are shaped like boomerangs, H^H, with slightly (-) charged O's in the heads and slightly (-) charged H's in the tails. The H's of molecules are attracted to the O's of others by the attraction of unlike charges. This intermolecular force lowers the vapor pressure of H2O. CCl4 is completely symmetrical, so there is no charge attraction of its molecules for one another.

CCl4 molecules must have some attraction for one another, or it would never liquefy. Here the intermolecular force is a much weaker one called van der Waals forces. This is a kind of "law of gravity" for molecules. The sheer mass of the molecules attracts them weakly to one another.

The most subtle intermolecular forces are those that allow helium molecules to liquefy. Here, van der Waals forces are too weak for something with an atomic weight of 4. The attraction is called London dispersion forces, after chemical physicist Fritz London who formulated them. Once in a great while, the electrons of a helium atom all rush to one side. For a zillionth of a second, that side is just a little bit (-) and the other side a little bit (+). The side that is (+) attracts the electrons of another He atom to it, and that He atom gets divided into (+) and (-) sides. Finally, the attraction of all the (+_) for all the (-) draws the He atoms together into a liquid at extremely low temperatures.

Answer 3

would the containment, and also temperature make a difference in the interaction?