NEETChemistryThermodynamicsMCQ+4 / −1
Choose the correct statement for the work done in the expansion and heat absorbed or released when 5 litres of an ideal gas at 10 atmospheric pressure isothermally expands into vacuum until volume is 15 litres :
- ABoth the heat and work done will be greater than zero
- BHeat absorbed will be less than zero and work done will be positive
- CWork done will be zero and heat will also be zero
- DWork done will be greater than zero and heat will remain zero
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Correct answer: C
Since it is isothermal, $\Delta \mathrm{T}=0$
$$\Delta \mathrm{U}=\mathrm{nC}_{\mathrm{v}} \Delta \mathrm{T}=0$$
Since expansion is taking place against vacuum
$$\begin{aligned} & P_{\text {ext }}=0 \\ & W=-P_{\text {ext }} \Delta V=0 \end{aligned}$$
From first law of thermodynamics,
$$\begin{aligned} & \Delta U=q+W \\ & 0=q+0 \\ & q=0 \end{aligned}$$
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