Two moles of an ideal gas expand freely and isothermally from $5 \mathrm{dm}^3$ to $50 \mathrm{dm}^3$. What…
Two moles of an ideal gas expand freely and isothermally from $5 \mathrm{dm}^3$ to $50 \mathrm{dm}^3$. What is the value of $\Delta \mathrm{H}$ ?
Zero kJ
$20 \mathrm{~kJ}$
$100 \mathrm{~kJ}$
$150 \mathrm{~kJ}$
Solution
A free expansion means expansion against zero opposing force. $\mathrm{P}_{\mathrm{ext}}=0$ and hence, $\mathrm{W}=0$
For isothermal process, $\Delta \mathrm{U}=0$.
$\Delta \mathrm{H}=\Delta \mathrm{U}+\mathrm{P} \Delta \mathrm{V}=\Delta \mathrm{U}-\mathrm{W}$
$\Delta \mathrm{H}=0-0=0 \mathrm{~kJ}$