Question

Consider the following statements and arrange in the order of true/false as given in the codes.
$S_1$: Unit of the molar entropy of a substance in SI system is Joule/ Kelvin.
$S_2$: The Molar entropy of vaporization of ice is -ve.
$S_3$: In an adiabatic free expansion, heat involved is zero and therefore entropy change will be zero.
$S_4$: At absolute zero temperature, the entropy of a perfectly crystalline substance is zero.

• A. T F F T
• B. T F T T
• C. F F F T
• D. F F T T

Answer 1

The correct option is C F F F T

$S_1:$ Entropy is the measure of degree of randomness of a system. It's SI unit is $j{K}^{-1}$ . Molar entropy is the entropy content of one mole of a substance.

Hence it's SI unit is $j{mol}^{-1}{K}^{-1}$.

Hence, $S_1$ is False.

$S_2:$ Entropy of Vaporization is the increase in entropy upon Vaporization. It will always be $(+)ve$ since degree of randomness increases.

Molar entropy of Vaporization=$△S_{vap}=\frac{{△H}_{vap}}{T_{vap}}>0$

Hence, $S_2$ is False.

$S_3:$ An adiabatic expansion in which gas is allowed to expand without actually doing work is called adiabatic free expansion

$E_{internal}=Q+W$

$Q$=Energy transferred as a result of heat

$W$=Energy transferred as a result of work

In adiabatic, $Q$=0 (1st law)

So, $E_{internal}=W$

In free expansion, $W$=0

Hence, $E_{internal}=0$

Entropy change $△S_{total}=△S_{system}=nRln\left(\frac{V_2}{V_1}\right)>0$

Hence, $S_3$ is False.

$S_4:$ Entropy is defined as the degree of randomness of a system. At absolute temperature, as the molecular motion stops. So, the randomness becomes zero

Hence entropy is zero

Hence, $S_4$ is True.