Latent Heat of Fusion Formula

Introduction to Latent Heat of Fusion

We often hear since childhood that a block of ice melts to give chilled water; we also talk about the water turning to steam, which is used for rotating turbines and generating electricity.

However, we come across the phenomenon when we study science. This article discusses the latent heat of fusion formulas.

So, latent heat of fusion is the amount of inner or latent heat a solid gains (melting) to transform into a liquid state or the liquid state to gaseous (boiling).

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Latent Heat of Fusion Meaning

Latent heat means the energy required to change an object’s state. Fusion means combination. Overall, latent heat of fusion means the added energy or heat because of which an object changes to another state.

Here, it is about the transformation of solid to liquid, which is melting, and liquid to a gaseous state, which is called the boiling process.

Heat and Temperature

Under the chapter on Thermodynamics, we represent a parameter heat by an English block letter ‘Q’. We often jumble the word ‘heat’ with ‘temperature’; however, these two terms have huge differences.

Heat is the effect of an object generating vibrations in particles inside the object. We also consider heat as the rise in entropy of particles or the kinetic energy of these under the effect of rising temperatures.

Temperature is something that can be both high and low, while heat is always rising.

Now, when the heat is latent, for example, you have an inner heat and when you sleep, your body reaches the Gibbs’ free energy state because that time your body loses heat and its temperature fall.

Latent Heat of Fusion Formula

So, the formula of latent heat of fusion is given by:

\[\Delta \]Q = mL, which is the required equation for the latent heat of fusion


\[\Delta \]Q = change in heat energy in Joules

m = mass in Kg

L = Specific latent heat of fusion

So, do you know what the specific latent heat of fusion is?

Specific Latent Heat of Fusion 

We define the specific latent heat as the energy required to transform or change the state of 1 kg of substance.

However, the specific latent heat of fusion is the energy needed to melt a kilogram of substance. 

There is another term called the specific latent heat of vaporization. We define the specific latent heat of vaporization as the energy required to boil or evaporate a kilogram of substance.

Specific Latent Heat of Fusion Formula

The formula of specific latent heat of fusion is given by:

Q = mL, which is the required specific latent heat of the fusion equation.

Specific Latent Heat of Fusion Equation

We define the specific latent heat of the fusion equation in the following manner:

If ‘m’ kg of solid substance changes to liquid state at a constant temperature, which is its melting point, the heat absorbed by the substance or the latent heat of fusion formula is given by:

Q = mL


L = specific latent heat of fusion of substance that is measured in Joule per kilogram or J/kg.

Latent Heat of Fusion

Latent heat of fusion is also named as enthalpy of fusion which can be defined as the energy amount needed to be supplied to the solid substance which comes in the form of heat in order to bring a change in its original physical state and then convert it into a liquid state. In the liquid state, the pressure of the environment is maintained at constant. Let us understand this with an example. The latent heat of fusion of water (1 kg) is the amount of heat that must be provided to convert 1 KG of ice by not changing the temperature of the environment. This is kept at zero degrees Celsius. We must know that the opposite of latent heat is the solidification heat or heat of solidification which can be defined as the energy which needs to be supplied to the liquid in order to create phase change and convert the liquid to solid form. The value of heat of solidification of a substance is equal to the magnitude of the latent heat but is represented by an opposite sign. This can be explained with an example. The energy absorbed by ice to become water which is a liquid phase is equal to the amount of energy produced by water to become ice. The latent heat is also used to describe the energy required for the accommodation of any increase in the volume of the substance after it changes its original state. Melting point is the temperature under which the substance has a phase transition and this point of transition or the temperature is also known as the freezing point of that substance when factors like heat or solidification are considered. Unless it is stated otherwise, when we express the latent heat of fusion, we assume the pressure of the environment to be 1 atmosphere of pressure which equals 101.325 kilopascals approximately.

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A matter transforms from one state to another because of a hidden heat, which is latent. If energy is added to rise by 1 kg, it is the specific latent heat of fusion. Both are measured in J/kg.

FAQs on Latent Heat of Fusion Formula

1. Define specific heat?

The word ‘specific heat’ talks about an object being heated specifically by one degree. So, basically, the specific heat capacity of a solid is defined as the amount of heat needed to raise the temperature of a unit mass of the substance by one degree. 

The unit for measuring the specific heat is J/kg-°C.

2. What do you mean by specific heat at constant volume and constant volume?

Specific Heat at Constant Volume and Constant Pressure are intensive properties denoted by \[c_{v}\] and \[c_{p}\], respectively; these properties are defined for pure, simple, and compressible substances.

3. Specify latent heat of fusion?

The energy needed to entirely separate the molecules, moving from liquid to gas is much greater than if you were just to reduce their separation from solid to liquid.

4. What is the specific and molar heat of fusion?

When we consider a unit mass of substance then the energy that is required to convert the substance into liquid when there is a constant pressure is called the specific heat of fusion for the substance taken into consideration. On the other hand, when there is a change of enthalpy on a per-mole basis calculation then the heat of fusion is called the molar heat of fusion of the substance.

5. What is reasonable heat?

Reasonable heat is also known as latent heat which is not a steady circumstance and it is not a stage change is considered. This phenomenon reflects the heat which moves around the item and the environment. This heat can be known as the adjustment in the item’s temperature.

6. What is the latent heat of vaporization?

The latent heat of vaporization is known as the measure of heat which is converted for 1 gram of fluid into a fume. This is done without changing the fluid’s temperature. This definition didn’t originate from Weast(1964) but originated from Webster’s New World Dictionary. It is expressed as Cal/gram and the heat of evaporation is known as the latent heat.

7. What is the enthalpy of fusion?

Enthalpy of fusion is also known as latent heat when we consider that heat energy is meant to change when the substance changes from solid to fluid at air pressure. This is the latent heat of fusion as, during the process, the temperature remains constant. This is a measurable quantity when a substance dissolves. When we use it in reference to a unit of mass then it is called the specific heat of fusion.

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