Question

What is meant by bulk phenomena?

Answer 1

Hint: The phenomena deals with the states of matter and the process of transformation. There are mainly three states of matter namely, solid, liquid and gas. The process of solid becoming a liquid is melting, liquid to gas is vaporisation and again the reverse process that is, gas to liquid is condensation and liquid to solid is solidification. There are special cases where a solid directly changes to gas without entering liquid phase is known as sublimation and the gas directly changes to solid without entering the liquid phase is known as deposition.

Complete answer:
There are two types of phenomena that exist based on the location of molecular activity. One is the surface phenomenon and the other is bulk phenomenon.
1.Surface phenomena: The surface phenomenon is a mechanism which includes only the surface of some object or substance.
Example - Evaporation
 2.Bulk phenomena: The bulk phenomenon is a phenomenon in which the whole object or substance is involved in the process.
Example – Boiling
In bulk phenomena the total molecules (including interior molecules along with surface molecules) in the system are involved. As we all know the temperature at which a liquid changes into gas or vapour is known as boiling point. It indicates the strength of intermolecular force of attraction. Greater the intermolecular force higher will be the boiling point.
 Boiling is the bulk phenomena while the rest are surface phenomena because in case of boiling, the whole system takes part in the convection of heat from the heat source to the surface of the system, thereby involving the bulk of the molecules. This phenomena can only occur at the boiling point of the liquid as all the particles inside the liquid gain adequate energy to change into vapour state. Evaporation involves only the surface molecules and the rest of the system remains unaffected. Hence boiling is known as bulk phenomena.

Note:
All the adsorption process is said to be a surface phenomenon as the accumulation of molecules of a substance is at the surface rather than in the bulk of a solid or liquid. And all the absorption process is said to be a bulk phenomenon as it involves the total particles of the system including the surface. Hence bulk phenomena become the most important and complex phenomena in states of matter.