Question

The unit of entropy is:
a. $J{{K}^{-1}}mo{{l}^{-1}}$
b. $k{{J}^{-1}}mo{{l}^{-1}}$
c. $kJmo{{l}^{-1}}$
d. $~{{J}^{-1}}{{K}^{-1}}mo{{l}^{-1}}$

Answer 1

Hint: Start by using the mathematical expression for calculation of entropy. Entropy is calculated by taking into consideration the temperature and heat of the system.

Complete answer:
Entropy is commonly denoted as S. It is a thermodynamic property. Entropy is a measurement of the degree of randomness or disorder in the system. Greater the degree of disorder, higher is the entropy.
Entropy (like other thermodynamic properties – internal energy (U), enthalpy (H) is a state function, independent of path.
Addition of heat thus, increases randomness. Therefore, S is directly proportional to heat (q).
Also, temperature (T) is a measure of average chaotic motion of particles in the system. The randomness is more Heat added to a system at lower temperature causes more randomness than when it is heated at higher temperature. Therefore, we can say S is indirectly proportional to T.
Hence, the relation between S, q and T for a reversible reaction is given as
$S={{q}_{rev}}/T$
SI Unit of heat (q) = $Jmo{{l}^{-1}}$
SI Unit of temperature (T) = $K$
SI Unit of Entropy = $Jmo{{l}^{-1}}/\text{ }K\text{ }=\text{ }J{{K}^{-1}}mo{{l}^{-1}}$

Therefore, the answer is option (a).

Note: At absolute zero ($0{}^\circ K$/$-273.15{}^\circ C$/$-460{}^\circ F$), the value of entropy is zero.
The total entropy change ($\Delta {{S}_{total}}$) for the system and surroundings of a spontaneous process is given by
$\Delta {{S}_{total}}~=\Delta {{S}_{system}}+\Delta {{S}_{surrounding}}~>\text{ }0$
When a system is in equilibrium, the entropy is maximum, and the change in entropy is zero. Hence, we can say that S for a spontaneous process increases till it reaches a maximum and at equilibrium, the change in entropy is zero.