Question

Calculate difference between $\Delta$H and $\Delta$U when $1$ mole of grey tin (density $=$ $5.75$ $g/{cm}^3$) changes to white tin (density $=$ $7.31$ $g/{cm}^3$ ) at 10 bar.Given: At 298 K, $\Delta$ H $=$ $+2.1$ kJ, atomic weight of $Sn$ $=$ $119$ amu)

• A. $-8.8J$
• B. $-4.4J$
• C. $-2.2J$
• D. $+4.4J$

Answer 1

Answer: (B)

$-4.4J$

$V_{grey}=\frac{119}{5.75}{cm}^3$
$V_{white}=\frac{119}{7.31}{cm}^3$
$\Delta H=\Delta U+\Delta \left(PV\right)$
$\Delta H-\Delta U=10\times {10}^5(V_{grey}-V_{white})\times {10}^{-6}$
$=[\frac{119}{7.31}-\frac{119}{5.75}]J$
$=119[\frac{1}{7.31}-\frac{1}{5.75}]J$
$=-4.43$

$=-4.4J$ .