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Heat and Thermodynamics question

2022 · Shift 1 · Q53
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Heat and Thermodynamics question

2022 · Shift 1 · Q53

JEE AdvancedPhysicsHeat and ThermodynamicsMCQ+3 / −1

List I describes thermodynamic processes in four different systems. List II gives the magnitudes (either exactly or as a close approximation) of possible changes in the internal energy of the system due to the process.

List-I List-II
(I) 10−3 kg10^{-3} \mathrm{~kg}10−3 kg of water at 100∘C100^{\circ} \mathrm{C}100∘C is converted to steam at the same temperature, at a pressure of 105 Pa10^{5} \mathrm{~Pa}105 Pa. The volume of the system changes from 10−6 m310^{-6} \mathrm{~m}^{3}10−6 m3 to 10−3 m310^{-3} \mathrm{~m}^{3}10−3 m3 in the process. Latent heat of water =2250  kJ/kg=2250\, \mathrm{~kJ} / \mathrm{kg}=2250 kJ/kg.
(P) 2 kJ2 \mathrm{~kJ}2 kJ
(II) 0.20.20.2 moles of a rigid diatomic ideal gas with volume VVV at temperature 500 K500 \mathrm{~K}500 K undergoes an isobaric expansion to volume 3 V3 \mathrm{~V}3 V. Assume R=8.0Jmol−1 K−1R=8.0 \mathrm{Jmol}^{-1} \mathrm{~K}^{-1}R=8.0Jmol−1 K−1.
(Q) 7kJ7 k J7kJ
(III) One mole of a monatomic ideal gas is compressed adiabatically from volume V=13 m3V=\frac{1}{3} \mathrm{~m}^{3}V=31​ m3 and pressure 2kPa2 \mathrm{kPa}2kPa to volume V8\frac{V}{8}8V​.
(R) 4 kJ4 \mathrm{~kJ}4 kJ
(IV) Three moles of a diatomic ideal gas whose molecules can vibrate, is given 9 kJ9 \mathrm{~kJ}9 kJ of heat and undergoes isobaric expansion.
(S) 5 kJ5 \mathrm{~kJ}5 kJ
(T) 3 kJ3 \mathrm{~kJ}3 kJ

Which one of the following options is correct?

  1. A
    I →\rightarrow→ T, II →\rightarrow→ R, III →\rightarrow→ S, IV →\rightarrow→ Q
  2. B
    I →\rightarrow→ S, II →\rightarrow→ P, III →\rightarrow→ T, IV →\rightarrow→ P
  3. C
    I →\rightarrow→ P, II →\rightarrow→ R, III →\rightarrow→ T, IV →\rightarrow→ Q
  4. D
    I →\rightarrow→ Q, II →\rightarrow→ R, III →\rightarrow→ S, IV →\rightarrow→ T
View written solutionFree

Correct answer: C

We compute the change in internal energy ΔU\Delta UΔU for each process.


1. Process I

Given:

  • Mass of water, m=10−3 kgm=10^{-3}\,\text{kg}m=10−3kg
  • Latent heat, L=2250 kJ/kg=2.25×106 J/kgL=2250\,\text{kJ/kg}=2.25\times 10^6\,\text{J/kg}L=2250kJ/kg=2.25×106J/kg
  • Pressure, P=105 PaP=10^5\,\text{Pa}P=105Pa
  • Volume change: ΔV=10−3−10−6=0.999×10−3 m3≈10−3 m3\Delta V=10^{-3}-10^{-6}=0.999\times 10^{-3}\,\text{m}^3\approx 10^{-3}\,\text{m}^3ΔV=10−3−10−6=0.999×10−3m3≈10−3m3

Heat supplied: Q=mL=10−3×2.25×106=2250 JQ=mL=10^{-3}\times 2.25\times 10^6=2250\,\text{J}Q=mL=10−3×2.25×106=2250J

Work done: W=PΔV=105×0.999×10−3≈100 JW=P\Delta V=10^5\times 0.999\times 10^{-3}\approx 100\,\text{J}W=PΔV=105×0.999×10−3≈100J

By first law: ΔU=Q−W=2250−100=2150 J≈2 kJ\Delta U=Q-W=2250-100=2150\,\text{J}\approx 2\,\text{kJ}ΔU=Q−W=2250−100=2150J≈2kJ

So, I→P\boxed{\text{I} \rightarrow \text{P}}I→P​


2. Process II

Given:

  • n=0.2n=0.2n=0.2 moles of rigid diatomic gas
  • Initial temperature T1=500 KT_1=500\,\text{K}T1​=500K
  • Isobaric expansion from VVV to 3V3V3V

At constant pressure, for an ideal gas: T∝VT\propto VT∝V So, T2=3T1=1500 KT_2=3T_1=1500\,\text{K}T2​=3T1​=1500K Thus, ΔT=1000 K\Delta T=1000\,\text{K}ΔT=1000K

For a rigid diatomic gas: CV=52RC_V=\frac{5}{2}RCV​=25​R

Hence, ΔU=nCVΔT\Delta U=nC_V\Delta TΔU=nCV​ΔT ΔU=0.2×52×8×1000\Delta U=0.2\times \frac{5}{2}\times 8 \times 1000ΔU=0.2×25​×8×1000 ΔU=0.2×20×1000=4000 J=4 kJ\Delta U=0.2\times 20\times 1000=4000\,\text{J}=4\,\text{kJ}ΔU=0.2×20×1000=4000J=4kJ

So, II→R\boxed{\text{II} \rightarrow \text{R}}II→R​


3. Process III

Given:

  • One mole monatomic ideal gas
  • Initial volume V1=13 m3V_1=\frac13\,\text{m}^3V1​=31​m3
  • Initial pressure P1=2 kPa=2000 PaP_1=2\,\text{kPa}=2000\,\text{Pa}P1​=2kPa=2000Pa
  • Final volume V2=V18V_2=\frac{V_1}{8}V2​=8V1​​
  • Adiabatic compression

For monatomic gas: γ=53\gamma=\frac53γ=35​

Using adiabatic relation: P1V1γ=P2V2γP_1V_1^\gamma=P_2V_2^\gammaP1​V1γ​=P2​V2γ​ P2=P1(V1V2)γ=2000×85/3P_2=P_1\left(\frac{V_1}{V_2}\right)^\gamma=2000\times 8^{5/3}P2​=P1​(V2​V1​​)γ=2000×85/3 Now, 85/3=(23)5/3=25=328^{5/3}=(2^3)^{5/3}=2^5=3285/3=(23)5/3=25=32 So, P2=2000×32=64000 PaP_2=2000\times 32=64000\,\text{Pa}P2​=2000×32=64000Pa

Initial internal energy: U1=32P1V1=32×2000×13=1000 JU_1=\frac32 P_1V_1=\frac32\times 2000\times \frac13=1000\,\text{J}U1​=23​P1​V1​=23​×2000×31​=1000J

Final internal energy: U2=32P2V2=32×64000×124=4000 JU_2=\frac32 P_2V_2=\frac32\times 64000\times \frac{1}{24}=4000\,\text{J}U2​=23​P2​V2​=23​×64000×241​=4000J (since V2=13×18=124V_2=\frac{1}{3}\times\frac18=\frac{1}{24}V2​=31​×81​=241​)

Thus, ΔU=U2−U1=4000−1000=3000 J=3 kJ\Delta U=U_2-U_1=4000-1000=3000\,\text{J}=3\,\text{kJ}ΔU=U2​−U1​=4000−1000=3000J=3kJ

So, III→T\boxed{\text{III} \rightarrow \text{T}}III→T​


4. Process IV

Given:

  • n=3n=3n=3 moles diatomic gas with vibration active
  • Heat supplied Q=9 kJQ=9\,\text{kJ}Q=9kJ
  • Isobaric expansion

For diatomic gas with vibration active:

  • Degrees of freedom f=7f=7f=7

CV=72R,CP=CV+R=92RC_V=\frac{7}{2}R, \qquad C_P=C_V+R=\frac{9}{2}RCV​=27​R,CP​=CV​+R=29​R

In isobaric process: Q=nCPΔTQ=nC_P\Delta TQ=nCP​ΔT ΔU=nCVΔT\Delta U=nC_V\Delta TΔU=nCV​ΔT So, ΔU=QCVCP=9×7292=9×79=7 kJ\Delta U=Q\frac{C_V}{C_P}=9\times \frac{\frac72}{\frac92}=9\times \frac79=7\,\text{kJ}ΔU=QCP​CV​​=9×29​27​​=9×97​=7kJ

Thus, IV→Q\boxed{\text{IV} \rightarrow \text{Q}}IV→Q​


5. Final matching

We obtained:

  • I→P\text{I} \rightarrow \text{P}I→P
  • II→R\text{II} \rightarrow \text{R}II→R
  • III→T\text{III} \rightarrow \text{T}III→T
  • IV→Q\text{IV} \rightarrow \text{Q}IV→Q

This matches: Option C\boxed{\text{Option C}}Option C​


6. Comparison with stored answer

Stored correct answer: C

Our derived answer: C

So the answer agrees with the stored answer.

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