For a monoatomic gas, the work done at constant pressure is ' $\mathrm{W}$ '. The heat supplied at constant…

For a monoatomic gas, the work done at constant pressure is ' $\mathrm{W}$ '. The heat supplied at constant volume for the same rise in temperature of the gas is
  1. $2 \mathrm{~W}$
  2. W
  3. $\frac{\mathrm{W}}{2}$
  4. $\frac{3 \mathrm{~W}}{2}$

Solution

At constant pressure, $\mathrm{W}=\mathrm{P} . \Delta \mathrm{V}$ For an ideal gas, $\mathrm{PV}=\mathrm{nRT}$ $\begin{aligned} & \therefore \mathrm{P} \Delta \mathrm{V}=\mathrm{n} \mathrm{R} \Delta \mathrm{T} \\ & \mathrm{W}=\mathrm{n} \mathrm{R} \Delta \mathrm{T} \end{aligned}$ Heat supplied at constant volume, $\begin{aligned} & \mathrm{Q}=\Delta \mathrm{U}=\mathrm{nC}_{\mathrm{v}} \Delta \mathrm{T}=\mathrm{n} \frac{3 \mathrm{R}}{2} \Delta \mathrm{T} \\ & \quad\left(\text { Formonoatomic gas } \mathrm{C}_{\mathrm{v}}=\frac{3}{2} \mathrm{R}\right) \\ & \therefore \mathrm{Q}=\frac{3 \mathrm{~W}}{2} \end{aligned}$

Asked in: MHT CET 2021 (23 Sep Shift 1)

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