Latent Heat Formula: Types of Latent Heat Transfer, and Importance

Latent heat is the amount of heat required to cause a phase transition. The main function of the atmosphere is to transfer energy in order to create equilibrium from pole to equator. To comprehend how the atmosphere keeps humans alive, we must first understand the processes of heat exchange in the atmosphere. Latent heat is the energy transmitted in the process of heat exchange or phase transition. In this section, we will understand the basic concepts of latent heat, types of latent heat and its importance. 

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Latent Heat

Latent heat is the amount of heat energy required per mass unit for a phase transition to occur. When we consider things on a molecular level, we can see that gaseous molecules have more vibration than liquid ones. 

When we add heat to a liquid, the molecules begin to vibrate. The energy required to alter the molecular mobility is referred to as latent heat. 

Every material has a different latent heat value.

Also Read: Specific heat capacity

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Latent Heat Formula

In physics, latent heat is the amount of heat required per kilogramme to change the state of an object. 

In the MKS (meter-kilogram-second) system, its units are joules per kilogramme (J/kg). 

A material's specific latent heat (L) is a measure of the thermal energy (Q) emitted or absorbed per mass (m) during a phase shift.

Mathematically, 

L = Q / M. 

Where,

• L = specific latent heat of a substance
• Q = amount of heat
• M = mass of the substance

This equation describes the amount of heat Q that must be added or withdrawn in order for a mass m item to change phases. L records the object's particular latent heat.

Also Read: 

Heat Formula

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Types of Latent Heat Transfer

Let’s discuss the types of latent heat transfer below in detail:

Latent Heat of Fusion- 

The heat consumed or emitted when matter melts, transitioning from solid to liquid at a constant temperature is referred to as latent heat of fusion. The heat energy required to convert the substance from solid to liquid at air pressure is the latent heat of fusion. 

The enthalpy change of any material as it dissolves is the latent heat of fusion.

When the heat of fusion is related to a unit of mass, it is referred to as the specific heat of fusion, whereas the molar heat of fusion refers to the enthalpy change per unit of material in moles. 

Latent Heat of Vapourization- 

The heat consumed or emitted when matter disintegrates, changing state from liquid to gas at a constant temperature is referred to as latent heat of vaporization. The most extreme known heat is the heat of vaporization of water. 

The heat of vaporization is defined as the amount of heat required to convert one gram of a fluid into a fume without causing the fluid's temperature to change. 

To be noted that latent heat is associated with no change in temperature but a change in condition. Because of the high heat of vaporization, disappearing water has an apparent cooling effect, whereas accumulation has a warming effect.

Latent Heat of Sublimation- 

Sublimation is a physical process in which a solid transforms directly to a gaseous (vapour) state without first passing through a liquid stage. 

The amount of heat required to turn a unit quantity of solid into gas at a given temperature is known as the latent heat of sublimation. 

When ice sublimates into vapour, for example, the amount of heat required at 0°C is calculated to be 2,838 kJ/kg, which is the ice's latent heat of sublimation at 0°C. 

Also Read: 

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Importance of Latent Heat

Latent Heat is energy in the form of heat that is emitted or absorbed by a material during a phase shift. The quantity of latent heat involved in condensation/evaporation and freezing/melting varies with temperature and pressure. Read on to learn more about the significance of latent heat:

1. As temperature rises, the latent heat of vaporization drops while the latent heat of fusion rises. Water is not the only material in the universe that exhibits three distinct phases at normal temperatures, but it is the most prevalent substance of this type on Earth. The phase shift of water involves a greater quantity of latent heat. The water cycle influences surface and atmospheric conditions, as well as atmospheric circulation, through the transmission of latent heat.
2. The atmosphere is a dynamic heat system that transports heat from one place to another. The latent heat associated in the phase shift of water is critical in the transmission of heat. Through a phase transition, the same amount of latent heat is released in the atmosphere as is absorbed at the Earth's surface. 
3. Latent heat is also an essential element in better understanding weather systems. Weather energy is supplied through latent heat. As water condenses, the latent heat from the water molecule is released into the air, heating it, making it lighter, and causing it to rise quickly. Some latent heat is converted into kinetic energy in this process, which enhances the speed of water molecules and powers up severe weather systems.

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Examples of Latent Heat

Everyday life is full of instances of latent heat:

1. When water boils on a stove, thermal energy from the heating element is transmitted to the pot and then to the water. When sufficient energy is applied, liquid water expands to produce water vapours and boils. When water boils, a tremendous quantity of energy is released. Because water vaporizes at such a high temperature, it is easier to be burnt by steam.
2. Similarly, substantial energy must be consumed in a freezer to turn liquid water to ice. The freezer eliminates thermal energy, which allows the phase change to take place. Freezing water needs more energy than freezing liquid oxygen into solid oxygen per unit gram because water has a high latent heat of fusion.
3. Hurricanes strengthen as a result of latent heat. When air passes over warm water, it warms up and takes up water vapour. Latent heat is released into the sky as the vapour condenses to create clouds. 

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Things to Remember Based on Latent Heat

• Latent heat is the amount of heat energy required per mass unit for a phase transition to occur.
• In the MKS (meter-kilogram-second) system, the unit of latent heat is joules per kilogramme (J/kg). 
• Mathematically, Latent Heat can be expressed as L = Q / M. Where, L is the specific latent heat of a substance, Q is the amount of heat and M is the mass of the substance
• Every phase transition occur at a certain temperature and at a specific pressure
• There is no change in temperature during a phase change.
• Latent heat can be released or absorbed.
• Heat is absorbed from the environment through endothermic phase transitions.
• Heat is released into the environment during exothermic phase transitions.
• The transition from liquid to solid is represented by the latent heat of fusion. 
• The transition from a liquid to a gas is represented by latent heat of vaporization.
• The transition from solid to gas is represented by the latent heat of sublimation. 

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