Answer
(a) $75.1\,JK^{-1}mol^{-1}$
Solid is changed to aqueous state which increases the randomness and therefore entropy increases. $\Delta_{r}S^{\circ}$ is positive because of this increase.
(b) $112.5\,JK^{-1}mol^{-1}$
The liquid is changed to gaseous state which increases mobility and randomness and therefore entropy increases. $\Delta_{r}S^{\circ}$ is positive because of this increase.
(c) $-95.26\,JK^{-1}mol^{-1}$
Gas is changed to liquid state which decreases mobility and randomness and therefore entropy decreases. $\Delta_{r}S^{\circ}$ is negative because of this decrease.
(d) $157.68\,JK^{-1}mol^{-1}$
Solid is changed to gaseous state which increases the randomness and therefore entropy increases. $\Delta_{r}S^{\circ}$ is positive because of this increase.
Work Step by Step
Recall: $\Delta_{r} S^{\circ}=\Sigma n_{p}S^{\circ}(products)-\Sigma n_{r}S^{\circ}(reactants)$
(a) $\Delta_{r} S^{\circ}=[S^{\circ}(NH_{4}Cl,aq)]-[S^{\circ}(NH_{4}Cl,s)]$
$=(169.9\,JK^{-1}mol^{-1})-(94.85\,JK^{-1}mol^{-1})$
$=75.1\,JK^{-1}mol^{-1}$
Solid is changed to aqueous state which increases the randomness and therefore entropy increases. $\Delta_{r}S^{\circ}$ is positive because of this increase.
(b) $\Delta_{r} S^{\circ}=[S^{\circ}(CH_{3}OH,g)]-[S^{\circ}(CH_{3}OH,l)]$
$=(239.7\,JK^{-1}mol^{-1})-(127.19\,JK^{-1}mol^{-1})$
$=112.5\,JK^{-1}mol^{-1}$
The liquid is changed to gaseous state which increases mobility and randomness and therefore entropy increases. $\Delta_{r}S^{\circ}$ is positive because of this increase.
(c) $\Delta_{r} S^{\circ}=[S^{\circ}(CCl_{4},l)]-[S^{\circ}(CCl_{4},g)]$
$=(214.39\,JK^{-1}mol^{-1})-(309.65\,JK^{-1}mol^{-1})$
$=-95.26\,JK^{-1}mol^{-1}$
Gas is changed to liquid state which decreases mobility and randomness and therefore entropy decreases. $\Delta_{r}S^{\circ}$ is negative because of this decrease.
(d) $\Delta_{r} S^{\circ}=[S^{\circ}(NaCl,g)]-[S^{\circ}(NaCl,s)]$
$=(229.79\,JK^{-1}mol^{-1})-(72.11\,JK^{-1}mol^{-1})$
$=157.68\,JK^{-1}mol^{-1}$
Solid is changed to gaseous state which increases the randomness and therefore entropy increases. $\Delta_{r}S^{\circ}$ is positive because of this increase.
