it is clear that in a liquid the forces between molecules are more important.
Because of this decreased volume and increased intermolecular interaction, a
liquid expands and contracts only very slightly with a change in temperature and
lacks the compressibility typical of gases.
Kinetics of Liquids
Even though the volume of space between molecules has decreased in a liquid
and the mutual attraction forces between neighboring molecules can have great
effects on the molecules, they are still in motion. This motion can be verified
under a microscope when colloidal particles are suspended in a liquid. The
particles’ zigzag path, called Brownian movement, indicates molecular motion
and supports the Kinetic-Molecular Theory.
TIP
An increase in temperature increases the average kinetic energy of the molecules.Increases in temperature increase the average kinetic energy of molecules
and the rapidity of their movement. This is shown graphically in Figure 22. The
molecules in the sample of cold liquid have, on the average, less kinetic energy
than those in the warmer sample. Hence, the temperature reading T 1 will be less
than the temperature reading T 2. If a particular molecule gains enough kinetic
energy when it is near the surface of a liquid, it can overcome the attractive forces
of the liquid phase and escape into the gaseous phase. This is called a change of
phase. When fast-moving molecules with high kinetic energy escape, the average
energy of the remaining molecules is lower; hence, the temperature is lowered.
Figure 22. Distribution of the Kinetic Energy of Molecules