Custom Search
PROPERTIES OF PURE SUBSTANCE
A substance that has a fixed chemical composition throughout is called a pure substance. Water, nitrogen, helium, and carbon dioxide, for example, are all pure substances. A pure substance does not have to be of a single chemical element or compound, however. A mixture of various chemical elements or compounds also qualifies as a pure substance as long as the mixture is homogeneous. Air, for example, is a mixture of several gases, but it is often considered to be a pure substance because it has a uniform chemical composition
PHASE CHANGE PROCESSES OF A PURE SUBSTANCE
There are many practical situations where two phases of a pure substance coexist in equilibrium. Water exists as a mixture of liquid and vapor in the boiler and the condenser of a steam power plant. The refrigerant turns from
liquid to vapor in the freezer of a refrigerator.
_
PHASE CHANGE PROCESSES OF A PURE SUBSTANCE
There are many practical situations where two phases of a pure substance coexist in equilibrium. Water exists as a mixture of liquid and vapor in the boiler and the condenser of a steam power plant. The refrigerant turns from
liquid to vapor in the freezer of a refrigerator.
_
PROPERTY DIAGRAM FOR PHASE CHANGE PROCESSES
1. T-v DIAGRAM
2. P-V DIAGRAM
3. The P-T DIAGRAM
THE P-V-T SURFACE
SATURATED LIQUID-VAPOUR MIXTURE
During a vaporization process, a substance exists as part liquid and part vapor. That is, it is a mixture of saturated liquid and saturated vapor. To analyze this mixture properly, we need to know the proportions of the liquid and vapor
phases in the mixture. This is done by defining a new property called the quality x as the ratio of the mass of vapor to the total mass of the mixture:
Thus in a mixture of Vf and Vg the relative proportions are as follows: