17-8) If you accept the idea that matter is made up of discrete atoms and molecu

Question

17-8)     If you accept the idea that matter is made up of discrete atoms and molecules, gases can be visualized as consisting of:

(1)        atoms or molecules in continual motion, colliding with each other and the walls of their container, and

(2)        very far apart on the average relative to their diameters.

(a)        In terms of your observations of gasses and of the work you did in section 17.11 what are the justifications for this mental picture or model?

(b)        Why does the identical model not work well for liquids and solids? What evidence do you have that the distances between molecules are not far apart relative to their diameters?

Explanation / Answer

I do not know which work you performed at the respective section, bu I give a hint:

(a) The brownian motion (and experiment) is the explanation and proof of the continuous, aleatory movement of gas molecules. It increases with the temp.

The interactions between the molecules of a gas are very weak. That's why they don't have a form, but "walk" randomly within the container. Adding to this reason the fact that the density of gases is very small (under normal atmospheric conditions), here comes the explanation why the distances between gas molecules are so large.

(b) The above-mentioned points do not apply for liquids and solids.

E.g., for liquids, the measurements proved that their densities are about 1000 higher than their densities in the vapour phase. This means that the distances between the molecules are much smaller than the distances between the molecules of a gas. From here: the interaction forces between liquid molecules are much higher than those between the interaction forces between gas molecules.

For solids these parameters are even higher (densities and interaction forces), and the molecules are packed much tighter............

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