1.0 Introduction
Distillation is a separating technique in which two liquids are separated at essentially the same temperature and pressure. It is also the term used to describe the operation where the vaporization of a liquid mixture yields a vapor phase containing more than one constituents and it is desired to recover one or more of this constituents in a nearly pure state.
It would probably be beneficial to define the terms that describe the process and related properties. Let us begin by describing the process by which a substance transformed from the condensed phase to the gas phase. For liquid, this process is called VAPORIZATION and for a solid it is called SUBMIATIN, both processes requires heat. All substances regardless whether they are liquids or solids are characterized by a vapor pressure.
The vapor pressure of a pure substance is the pressure exerted by the substance against the external pressure which is usually atmospheric pressure. Vapor pressure is a measure of the tendency to escape. When the vapor pressure of a liquid substance reaches the external pressure the substance is observed to Boil. If the external pressure is atmospheric pressure, the temperature at which a pure substance boils is called the NORMAL BOILING POINT.
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