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Thermodynamics — Chemistry STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceChemistryThermodynamics2 Marks
Question
The enthalpy change for the reaction, $\text{Zn(s)}+2\text{H}^+(\text{aq})\overrightarrow{\ \ \ \ \ \ } \ \text{Zn}^{2+}(\text{aq})+\text{H}_2(\text{g}),$ is $-154.40 \mathrm{~kJ} \mathrm{~mol}^{-1}$. The formation of 2g of hydrogen expands the system by 22.4L at 1atm pressure.
What is the internal energy change of the reaction?
✓

Answer

Taking the initial volume as negligible (as no gaseous reactant is present), change in volume during expansion $(\Delta\text{V})=22.4\text{L}.$External pressure $\left(\mathrm{P}_{\mathrm{ext}}\right)$ = 1atm$\Delta\text{H}=\Delta\text{U}+\text{p}\Delta\text{V}$
$\Delta\text{U}=\Delta\text{H}-\text{p}\Delta\text{V}$
$\text{p}\Delta\text{V}=1\text{atm}\times22.4\text{L}=22.4\text{L atm}$
$=22.4\times101.3\text{J}=2307\text{J}=2.31\text{kJ}$
$\therefore\Delta\text{U}=-154.4-2.31=-156.71\text{kJ}$

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