Evaporation vs Distillation
Conversion from a liquid phase to the gaseous phase can take place in different paths like evaporation or vaporization at the boiling point. These two require different conditions.
Evaporation is the process of changing a liquid into its vapor stage. The word “evaporation” is specifically used when the vaporization happens from the surface of the liquid. Liquid vaporization can also happen at the boiling point where evaporation happens from whole liquid mass, but then it is not called as evaporation. Evaporation can be influenced by various factors like concentration of other substances in the air, surface area, pressure, temperature of the substance, density, flow rate of air etc.
Distillation is a physical separation method which is used to separate compounds from a mixture. It is based on the boiling points of the components in the mixture. When a mixture has different component with different boiling points, they evaporate at different times when we are heating. This principle is used in the distillation technique. If there are two substances in the mixture as A and B, we will assume A has the higher boiling point. In that case, when boiling, A will evaporate slower than B; therefore, the vapor will have a higher amount of B than A. Therefore, the proportion of A and B in the vapor phase is different from the proportion in the liquid mixture. The conclusion is that, the most volatile substances will be separated from the original mixture whereas, less volatile substances will remain in the original mixture.
In a laboratory, a simple distillation can be carried out. When preparing an apparatus, a round bottom flask should be connected to a column. End of the column is connected to a condenser and cold water should be circulated in the condenser so that when vapor travels through the condenser it gets cooled. Water should travel in the opposite direction of the vapor which allows maximum efficiency. The end opening of the condenser is connected to a flask. The entire equipment should be air sealed so that the vapor won’t escape during the process. A heater can be used to supply the heat to the round bottom flask which contains the mixture to be separated. When heating the vapor moves up the column and goes into the condenser. When it travels inside the condenser, it becomes cool and liquefies. This liquid is collected to the flask kept at the end of the condenser, and it is the distillate.
What is the difference between Evaporation and Distillation?
• In the distillation method, vaporization takes place at the boiling point whereas, in evaporation, vaporization takes place below the boiling point.
• Evaporation takes only from the surface of the liquid. In contrast, distillation is taking place from the whole liquid mass.
• At the boiling point of the distillation process, the liquid forms bubbles and there is no bubble formation in evaporation.
• Distillation is a separation or purifying technique, but evaporation is not necessarily so.
• In distillation, heat energy should be supplied to liquid molecules to go in to the vapor state but, in evaporation, an external heat is not supplied. Rather, molecules get energy when they collide with each other, and that energy is used to escape to the vapor state.
• In distillation, the vaporization happens rapidly, whereas the evaporation is a slow process.