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What is Latent heat of fusion?

The amount of heat energy required to change 1 kilogram of solid to liquid at atmospheric pressure at its melting point is known as the Latent heat of fusion.

What is Latent heat of vaporisation?

The amount of heat energy required to change 1 kilogram of liquid to gas at atmospheric pressure at its boiling point is known as Latent heat of vaporisation.

Types of vaporisation

Depending at the temperature at which a liquid changes to its vapour state, there are two types of vaporisation:

• Boiling: Liquid changing to vapour state at its boiling point is known as
• Evaporation: Liquid changing to vapour state at any temperature below its boiling point is known as

For example, the boiling point of water is [latex] 100^{\circ} [/latex] Celsius, but when wet clothes are put out to dry, the water is lost without it reaching its boiling point.

During evaporation, the particles of matter in the top layer possess more kinetic energy than the particles in the lower layer. Due to this, they are able to break away from the binding force faster. This results in quick evaporation of the topmost layers.

Evaporated particles are converted to the liquid state by cooling.

For example, droplets of water form on the surface of an object taken out of the refrigerator because the particles of water vapour lose energy and are converted into liquid.

What are the factors affecting evaporation?

There are four factors that affect the rate of evaporation.

(i) Surface area

Greater the surface area, the greater is the rate of evaporation.

For example, water in a flat pan will evaporate quicker than water in a glass

(ii) Temperature

Temperature and the rate of evaporation are directly proportional to each other. The higher the temperature, the higher will be the rate of evaporation.

For example, wet clothes dry quicker under the hot sun, than in the shade.

(iii) Humidity

Higher the rate of humidity, lower the rate of evaporation.

For example, during the monsoons the humidity in the air is far greater, that is the air contains a lot of water vapour. It, therefore, has very little space to hold any more water vapour. Therefore, during monsoons clothes take a longer time to dry.

(iv) Wind speed

Greater the wind speed, higher is the rate of evaporation.

For example, when clothes are dried when it is windy, they dry faster as the winds carry away the moisture and water vapour which is present in the air. This increases the rate of evaporation