Latent Heat of Water - Definition, Types, Formula , FAQs

Consider a block of ice of $0^{\circ }\mathrm{C}$. If you heat it the ice starts to turn into water but the temperature of the water only increases when all the ice has been changed into water. The same way when you heat water to ${100}^{\circ }\mathrm{C}$ the temperature does not change as the water boils and turns into steam. This phenomenon occurs due to latent heat. Let's explore the concept of Latent heat in detail.

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This Story also Contains

1. Latent heat
2. Latent Heat of Water
3. Types of Latent Heat of water

Latent heat

Latent heat is defined as heat emitted or absorbed by a substance during the change of phase and without a temperature change. Here the phase change is the transition from liquid to solid or gas, a transition from solid to liquid or gas, and the transition from gas to solid or liquid. Generally, latent heat is represented in joules or calories in unit mass.

Latent Heat of Water

Latent heat of water is heat required for phase change of water without change in temperature of water. Here phase change is transition of water to ice or vapor, ice to water or vapor. When there is transition of state from liquid to solid and gas to liquid, during that time heat will be released (exothermic). When there is transition of state from liquid to gas and solid to liquid, during that time heat will be absorbed (endothermic).

S.I. unit of latent heat is given by J/Kg.

Formula to Calculate Latent Heat

$\mathrm{L}=\mathrm{Q}/\mathrm{M}$

Where,

• Q is the heat quantity
• M is the body mass
• L is latent heat

This equation states that the amount of heat released or absorbed by the substance of mass M gives as latent heat.

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Types of Latent Heat of water

Generally latent heat of water is of two types:

1. Latent heat of fusion
2. Latent heat of vaporization

Latent heat of fusion:

Latent heat of fusion refers to melting a solid and freezing a liquid without change in temperature. Here melting a solid means melting ice (transition of solid phase to liquid phase), and freezing a liquid means cooling down a liquid to ice (transition of the liquid phase to solid phase).

Example of latent heat of fusion

When you take ice at 0°C and supply heat to it, the temperature does not change immediately. Instead, the heat is used to break the connections of the ice molecules which transforms it from a solid to liquid phase.

This heat, absorbed without a change in temperature, is called the latent heat of fusion.

In practical terms: You could say that in order to completely melt 1 kilogram of ice, into water, 334,000 joules of energy is required.

Latent heat of vaporization of water:

Latent heat of vaporization refers to boiling a liquid and condensing a gas without change in temperature. Here boiling a liquid means we are going to heat the water (transition of liquid phase to gas phase) and condensing a gas means we are going to cool or condense the evaporated water (transition of gas phase to liquid phase).

Example of latent heat of vaporization of water

Consider a bucket of water boiling at 100-degree Celsius, the amount of energy required to change water to vapor is 540 Cal/g. Similarly, the energy required to condense the vapor back to water is -540cal/g. So, the latent heat of vaporization of water is 2257 kJ/kg.

Practical Example: While boiling water in a kettle, the heat from the stove is absorbed by the water. After the water hits the boiling point of 100°C the heat doesn’t raise the temperature of the water but rather contributes to changing the water into steam.

Specific latent heat

Specific latent heat is defined as the amount of heat required for transition of one phase completely to another phase for a unit mass. The heat capacity of a particular substance depends upon the mass of that substance. However, the specific heat capacity (s) does not depend on the mass of the substance.
Specific heat capacity is defined as at constant pressure the amount of heat required to increase the temperature to 1 degree Celsius for 1 gram of substance. Specific latent heat is represented in J/Kg. This can be given by increasing the temperature to 1 degree Celsius for 1 gram of water, we require 4.186J of heat or 1 calorie. To calculate the heat required for a change in temperature we can use this equation:

$q=m\times s\times \mathrm{\Delta }t$

Where,

• q is heat required
• m is mass of substance
• s is specific heat
• ∆t change in temperature

This equation cannot be used when transition of phase takes place.