temperature change difference between final and initial temperature.

triple point temperature and pressure at which solid, liquid, and gaseous states of a substance coexist and remain at equilibrium with one another. A unique point on a phase diagram.

vaporization process of going from liquid (and sometimes solid) to gaseous state.

vapor pressure pressure exerted by vapor molecules in equilibrium with corresponding liquid or solid. viscosity resistance of a liquid to flow.

volatile liquid liquid that readily evaporates. Indicates weak intermolecular forces.

volume the amount of space occupied by a system. The amount of room it takes up.

warming curve curve plotting temperature as a function of either energy added or time.

Vapor Pressure

Lubricating greases have very low vapor pressures due mainly to the high molecular masses of their molecules. Consider how long one would expect to wait to see a container of lubricating grease completely ÒvaporizeÓ while resting open in the family garage.

But in outer space, the atmospheric pressure is so low that the vapor pressure of normal lubricating grease is higher than this low atmospheric pressure. Thus, normal lubricants rapidly boil away and the ensuing friction causes machinery to fail. Needless to say, special lubricants have been developed for use in our space program.

Clothing can be dried on the clothesline even in the winter when the ambient temp-erature is below freezing because water has vapor pressure even when solid (4.6 mm Hg at 0°C). At temperatures below freezing, the moisture in the clothing sublimes away.

The fact that water has substantial vapor pressure in the solid state explains why one must wrap steaks in a Òzip lockÓ bag or other tight wrap to preserve the water content. Failure to protect the steak may lead to freezer burn or a dry Òbeef jerkyÓ steak.

Under prevailing atmospheric pressure, dry ice (solid CO 2 ) sublimes to the gaseous state. The triple point pressure of carbon dioxide is above atmospheric pressure. Under normal conditions, liquid carbon dioxide will never be seen.

Fruit juice concentrates which can be purchased frozen at grocery stores are concentrated by boiling the major portion of the water out of the Òfresh squeezedÓ juice. If the boiling were done at normal atmospheric pressures, the high temperature would destroy molecules which provide the fresh flavor. Vats of juice are placed under a partial vacuum and boiling takes place at a lower temperature. The molecules are not denatured but are preserved to provide taste at the breakfast table.

Everyone has heard of freeze dried coffee. Interestingly, this same technique can be applied in taxidermy. The animal specimen to be preserved is first carefully frozen. Then the specimen is placed in a vacuum chamber and the atmospheric pressure is lowered until the ice in the tissue sublimes away. Shrinkage and distortion of the specimen, which occur under normal drying techniques, are reduced to a minimum.

The white granulated sugar purchased at your local grocery store is produced by heating sugar syrup solution under a vacuum until it becomes supersaturated and deposits crystals around ÒseedÓ crystals. Heating under a vacuum reduces the operating temperature and minimizes discoloration (caramelization) due to decomposition of the sugary syrup.

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