Question

Calculate the total entropy change for the transition at $368K$ of 1 mol of sulphur from the monoclinic to the rhombic solid state. Given $△H$ = $-401.7Jmo{l}^{-1}$ for the transition. Assume the surrounding to be an ice-water bath at $0^{\circ }C$.

• A. $-1.09J{K}^{-1}$
• B. $1.47J{K}^{-1}$
• C. $0.38J{K}^{-1}$
• D. None of these

Answer 1

The correct option is C $0.38J{K}^{-1}$

We know entropy change for phase transition (for 1 mol here) is given as:
$△S_{\left(system\right)}=\frac{\Delta H_{trans}}{T}=\frac{1\times -401.7}{368}=-1.09J{K}^{-1}$

The heat given out by system is absorbed by ice-water bath at $273K$

$\therefore △S_{surrounding}=\frac{1\times 401.7}{273}=1.47J{K}^{-1}so,△S_{\left(total\right)}=△S_{sys}+△S_{surr}=-1.09+1.47=0.38J{K}^{-1}$