Question

The unit of latent heat is
A) cal-g
B) $ cal/^oC $
C) cal/g
D) None of these

Answer 1

Hint The latent heat is the amount of heat energy required to convert the phase of a given material of unit mass. Use the formula of latent heat energy to determine the unit of latent heat

Formula used:
 $\Rightarrow Q = mL $ where $ Q $ is the heat energy used to convert a material’s state of mass $ m $ having latent heat $ L $

Complete step by step answer
The latent heat of a material corresponds to the amount of energy required per unit mass of the substance to change its state, e.g. ice to water. Latent heat can also be understood as energy in a hidden form that is supplied or extracted to change the state of a substance without changing its temperature. Hence the amount of heat energy to convert mass $ m $ can be calculated using
 $\Rightarrow Q = mL $
In the above equation, $ Q $ is the heat energy and it has the dimensions of calories (cal) in the CGS scale. And, $ m $ is the mass of the substance which has the units grams (g). So, the latent heat can be calculated as
 $\Rightarrow L = \dfrac{Q}{m} $ which has the units
$ L = \dfrac{{cal}}{g} = cal/g $ which corresponds to option C.

Note
We must be careful in not confusing latent heat with specific heat capacity which is the energy required to change the temperature of a unit mass of a substance by a unit temperature without changing its phase. While here, we have found the units in the CGS unit as cal/g, the unit of latent heat can be represented in other unit systems. In the SI unit system, the unit of latent heat is Joules/kg.