Question

Define (i) Evaporation (ii) Latent heat of fusion

Answer 1

Evaporation is the process in which the liquid turns into vapors. It is the main process through which water returns back to water cycle as atmospheric vapor. Latent heat is known as the heat of transformation, the word latent means hidden as it is the hidden energy required to change the state of a substance at constant temperature conditions.

Complete Step By Step Solution:
(i) Evaporation: The process of changing of water from liquid to vapor or gaseous state is known as Evaporation. It is quite an important part of our water cycle. Heat energy is important for the process of evaporation as it imparts energy to the water molecules making them vibrate quickly to turn into the atmospheric vapors. This energy is used to break the bond of water molecules and leads to an easy evaporation at the boiling point. During evaporation heat is removed from the environment which provides a net cooling effect.
Factors affecting evaporation are- Temperature: The more is the temperature, the more energy is imparted to the water molecules causing them to break their bonds and escape as atmospheric vapors.
Surface Area: More is the surface area of a liquid the more will be its evaporation.
Dryness: Dryness can also lead to increase in evaporation rate as compared to humid conditions.
(ii) Latent heat of Fusion: Latent heat is the heat of transformation which is required to change the state of a substance but without changing its temperature. Latent heat of fusion is the change in enthalpy when any amount of substance melts. Enthalpy determines the heat added or removed from the substance when it changes at constant pressure. The latent heat is given by the expression, Q = mL
Where Q is the heat energy released or absorbed during phase change, m is the mass of substance and L is the latent heat. It's S.I. units are joule per kilogram.

Note: The process opposite to evaporation is known as Condensation. It is the transition from gaseous state to liquid state. The latent heat of fusion for water is $80$ cal/g. There also exists a Latent heat of Vaporization which is used to convert a substance from liquid to gaseous state at constant temperature conditions. Latent heat is normally expressed in joules or calories per mass of the substance undergoing transformation.