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 = $$Jmo{l}^{-1}/K=J{K}^{-1}mo{l}^{-1}$$

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 ($$\mathrm{\Delta }{S}_{total}$$) for the system and surroundings of a spontaneous process is given by
$$\mathrm{\Delta }{S}_{total}=\mathrm{\Delta }{S}_{system}+\mathrm{\Delta }{S}_{surrounding}>0$$
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.