A gas expands isothermally against a constant external pressure of 1 bar from $10 \mathrm{dm}^3$ to $20 \mathrm{dm}^3$ by absorbing 800 J of heat from surrounding. Calculate value of $\Delta \mathrm{U}$.

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Aicharya · Accepted Answer

$\begin{aligned} & \mathrm{P}_{\mathrm{ext}}=1 \mathrm{bar} \ & \mathrm{V}_1=10 \mathrm{dm}^3, \mathrm{~V}_2=20 \mathrm{dm}^3 \ & \mathrm{Q}=800 \mathrm{~J} \ & \mathrm{~W}=-\mathrm{P}_{\mathrm{ext}}\left(\mathrm{V}_2-\mathrm{V}_1ight)=-1 \mathrm{bar}\left(20 \mathrm{dm}^3-10 \mathrm{dm}^3ight) \ & \quad=-10 \mathrm{dm}^3 \mathrm{bar}=-1000 \mathrm{~J} \ & \Delta \mathrm{U}=\mathrm{Q}+\mathrm{W}=800 \mathrm{~J}-1000 \mathrm{~J}=-200 \mathrm{~J}\end{aligned}$

A gas expands isothermally against a constant external pressure of 1 bar from $10 \mathrm{dm}^3$ to $20…

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