Question

Define latent heat of fusion.

Answer 1

In order to solve this question our theory should be strong and confirmed so Latent heat of fusion, also known as enthalpy of fusion, is the amount of energy that must be supplied to a solid substance in order to trigger a change in its physical state and convert it into a liquid.

Complete answer:
Latent heat, energy absorbed or released by a substance during a change in its physical state (phase) that occurs without changing its temperature. The latent heat is normally expressed as the amount of heat (in units of joules or calories) per mole or unit mass of the substance undergoing a change of state.
$L = \dfrac{Q}{m}$
Where: L is latent heat of substance ,Q is energy released or absorbed during phase and m is the mass.

Now we should understand latent heat of fusion:
Latent heat of fusion, also known as enthalpy of fusion, is the amount of energy that must be supplied to a solid substance (typically in the form of heat) in order to trigger a change in its physical state and convert it into a liquid (when the pressure of the environment is kept constant). For example, the latent heat of fusion of one kilogram of water, which is the amount of heat energy that must be supplied to convert 1 kg of ice without changing the temperature of the environment (which is kept at zero degrees celsius) is 333.55 kilojoules.

It can be noted that the opposite of latent heat of fusion is the heat of solidification, which is the amount of energy that must be supplied to a liquid in order to facilitate a phase change and the conversion of the liquid into a solid. It can also be noted that the value of the heat of solidification of a substance is always equal in magnitude to the latent heat of fusion but always bears an opposite sign. For example, the amount of energy absorbed by ice to become water is equal to the amount of energy liberated by water to become ice.

The latent heat of fusion of a substance also accounts for the energy required to accommodate any increase in the volume of the substance post the change of its physical state. The temperature at which the substance undergoes the phase transition is called the melting point of the substance. This temperature point can also be referred to as the freezing point of the substance when the heat of solidification is being considered. Unless specified to be otherwise, the pressure of the environment (when expressing the latent heat of fusion of a substance) is always assumed to be 1 atmosphere of pressure.

Note: Rather than these there are two more specific heat and molar heat of fusion so we will be studying these also:If unit mass of the substance is considered, the energy required to convert it into a liquid under constant pressure is called the specific heat of fusion for the substance. If the change in enthalpy is calculated on a per-mole basis, the latent heat of fusion is referred to as the molar heat of fusion of the substance.