Concept:

Latent heat: It is the amount of heat needed to change the state of a unit mass of any substance without changing its temperature.

i.e., we can say that heat needed to supply for changing its state will be directly proportional to the mass m of the substance.

∴Q ∝ m

i.e.,Q = mL

The SI unit of Latent heat is J/Kg and the CGS unit is Cal/g respectively.

Where,

m = mass of an object

L = Latent heat

Q = amount of heat needed to change the state of matter of mass m 

Explanation:

From the above explanation, we can see that Amount of heat needed to melt a unit mass of a substance is directly proportional to the amount of mass of an object since the Latent heat of a material is constant.

i.e., Q ∝ m ⇒ Q = mL

Thus the unit of latent heat can be expressed as \(L=\frac{Q}{m}\Rightarrow L=\frac{Joules}{kg}\)