Boiling vs. Evaporating

Difference Between Boiling and Evaporating

Boiling and evaporating are the terms in physics. They are used in our daily life to refer to physical properties of an object. There is fundamental difference between the two. Many people wrongly think that they are the same terms. Let us discuss boiling and evaporating one by one to know the difference between the two terms.

Boiling point

The temperature at which the liquid pressure of a substance equals the external pressure is called the boiling point. At this temperature the vapor pressure of a liquid is equal to the external pressure forming the bubbles.

Vapor pressure should be explained before understanding boiling point. Vapor pressure is the identification of liquid’s rate of evaporation. All liquids evaporate into gases. In the process of evaporation, the molecules of a liquid have a tendency to escape from the surface of liquid. The liquids having higher vapor pressure evaporate quickly and are called volatile. Petrol is the example of such liquid.  At boiling point is the temperature at which a liquid begins to boil. It is the temperature at which the vapor pressure equals the atmospheric pressure. It allows the molecules of the liquid to quickly evaporate into atmosphere. When water is heated, its vapor pressure increases and it begins to boil.

Evaporation

In the process of evaporation molecules of liquid turns into gases in the absence of heat. Some liquids such as petrol have such properties that they evaporate when they are kept open in atmosphere. Molecules of such liquids remain in the random motion and keep colliding with each other. As a result of this collision, energy transfers to those molecules which are on the surface and they escape in the atmosphere. The process is called evaporation.

In the process of evaporation, boiling takes place without heating. If the volatile liquids are kept inside the container, the molecule cannot escape and evaporation does not take place. The air in the container is saturated and it is stage of equilibrium.

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