Question

Unit of entropy is:
A.${\text{J}}{{\text{K}}^{ - 1}}{\text{mo}}{{\text{l}}^{ - 1}}$
B.${\text{Jmo}}{{\text{l}}^{ - 1}}$
C.${{\text{J}}^{ - 1}}{{\text{K}}^{ - 1}}{\text{mo}}{{\text{l}}^{ - 1}}$
D.${\text{JKmo}}{{\text{l}}^{ - 1}}$

Answer 1

Hint:To answer this question, you must recall the mathematical expression used for the calculation of entropy. Entropy for a system is calculated using the temperature and heat of the system.

Complete answer:
We know that addition of heat to a system increases the energy of the particles in the system and thus resulting in an increase in randomness. Hence, we can conclude that entropy is directly proportional to heat (represented by q). Temperature (T) too is a measure of the chaos caused by the motion of particles in the system. In other words, heat added to a system at lower temperatures causes more disorder in the system than that in the case of a system at higher temperature. Thus, we can conclude that entropy is inversely proportional to temperature of a system.
So, we can write the relation between the entropy heat and temperature of a system as,
 $S = \dfrac{q}{T}$
We know that the units of heat and temperature are ${\text{Jmo}}{{\text{l}}^{ - 1}}$and ${\text{K}}$respectively.
Thus, the unit for entropy will be${\text{J}}{{\text{K}}^{ - 1}}{\text{mo}}{{\text{l}}^{ - 1}}$.

Thus, the correct answer is A.

Note:
Entropy is the measure of the degree of disorder or randomness in a system. It is a thermodynamic property and is represented using the alphabet S. Greater is the degree of randomness in a system, higher will be its entropy. Like other thermodynamic properties, namely internal energy (U), free energy (G), enthalpy (H), etc., entropy too is a state function. Its value is independent of the path followed by reaction and depends only on the initial and final states of the system.