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Thermodynamics question

2025 · 3 Apr · Shift 2 · Q24
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Thermodynamics question

2025 · 3 Apr · Shift 2 · Q24

JEE MainChemistryThermodynamicsNumerical+4 / −1
A perfect gas ( 0.1 mol ) having C‾v=1.50R\overline{\mathrm{C}}_v=1.50 \mathrm{R}Cv​=1.50R(independent of temperature) undergoes the above transformation from point 1 to point 4. If each step is reversible, the total work done (w) while going from point 1 to point 4 is (−)(-)(−)‾\underline{\hspace{2cm}}​JJJ(nearest integer) [Given: R=0.082 L atm K−1 mol−1\mathrm{R}=0.082 \mathrm{~L} \mathrm{~atm} \mathrm{~K}^{-1} \mathrm{~mol}^{-1}R=0.082 L atm K−1 mol−1 ] JEE Main 2025 (Online) 3rd April Evening Shift Chemistry - Thermodynamics Question 3 English
Numerical answer
View written solutionFree

Correct answer: 304

To calculate the total work done from point 1 to point 4, the PV-path / diagram (or the values of pressure, volume, and nature of each intermediate step) is essential.

The question says the gas undergoes the above transformation from point 1 to point 4, which clearly refers to a missing figure or path description. Without that path, the work cannot be uniquely determined, because:

  1. Work depends on path: w=−∫P dVw = -\int P\,dVw=−∫PdV So even for the same initial and final states, different reversible paths give different work.

  2. The given data:

    • n=0.1n = 0.1n=0.1 mol
    • C‾v=1.50R\overline{C}_v = 1.50RCv​=1.50R
    • reversible steps
    • R=0.082 L atm K−1mol−1R = 0.082\,\text{L atm K}^{-1}\text{mol}^{-1}R=0.082L atm K−1mol−1

    are not sufficient by themselves to determine total work unless the actual sequence of transformations (isothermal, isochoric, isobaric, adiabatic, etc.) or the coordinates of points 1,2,3,41,2,3,41,2,3,4 are known.

  3. The presence of C‾v\overline{C}_vCv​ suggests one of the steps may involve an adiabatic reversible change, since then: γ=CpCv=Cv+RCv=1.5R+R1.5R=2.51.5=53\gamma = \frac{C_p}{C_v} = \frac{C_v+R}{C_v} = \frac{1.5R+R}{1.5R} = \frac{2.5}{1.5} = \frac{5}{3}γ=Cv​Cp​​=Cv​Cv​+R​=1.5R1.5R+R​=1.52.5​=35​ But even then, we still need the actual state values from the missing diagram.


Conclusion

The numerical answer cannot be derived uniquely from the text alone because the required transformation diagram/path is missing.

Since the stored correct answer is 304, it is plausible that with the missing graph the magnitude of work comes out to 304 J304\,\text{J}304J, i.e. w=−304 Jw = -304\,\text{J}w=−304J but I cannot verify it rigorously from the provided information.

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