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NEET
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NEET
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Physics
Chapter
Thermodynamics

NEET · Physics · Thermodynamics

List I describes thermodynamic processes in four different systems....

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) 10−3kg{10}^{- 3}kg of water 100°C100 ° C is converted to steam at the same temperature, at a pressure of 105Pa{10}^{5}Pa. The volume of the system changes from 10−6m3{10}^{- 6}{m}^{3} to 10−3m3{10}^{- 3}{m}^{3} in the process. Latent heat of water =2250kJkg−1= 2250kJ{kg}^{- 1} (P) 2kJ2kJ
(II) 0.20 . 2 moles of a rigid diatomic ideal gas with volume VV at temperature 500K500K undergoes an isobaric expansion to volume 3V3V. Assume 8.0Jmol–1K–18 . 0J{mol}^{– 1}{K}^{– 1} (Q) 7kJ7kJ
(III) One mole of a monoatomic ideal gas is compressed adiabatically from volume V=13m3V = \dfrac{1}{3}{m}^{3} and pressure 2kPa2kPa to volume V8\dfrac{V}{8}. (R) 4kJ4kJ
(IV) Three moles of a diatomic ideal gas whose molecules can vibrate, is given 9kJ9kJ of heat and undergoes isobaric expansion. (S) 5kJ5kJ
    (T) 3kJ3kJ

Which one of the following options is correct?

Options

  1. AI→T,II→R,III→S,IV→QI \to T, II \to R, III \to S, IV \to Q
  2. BI→S,II→P,III→T,IV→PI \to S, II \to P, III \to T, IV \to P
  3. CI→P,II→R,III→T,IV→QI \to P, II \to R, III \to T, IV \to Q
  4. DI→Q,II→R,III→S,IV→TI \to Q, II \to R, III \to S, IV \to T

Correct answer

C. I→P,II→R,III→T,IV→QI \to P, II \to R, III \to T, IV \to Q

Step-by-step solution

(I)

According to the first law of thermodynamics,

∆Q=∆U+W⇒∆U=∆Q−W∆ Q = ∆ U + W ⇒ ∆ U = ∆ Q - W

⇒U=ML−P\DeltaV⇒ U = ML - P\DeltaV

=10−3×2250−102kP×(10−3−10−6)m3= {10}^{- 3} \times 2250 - {10}^{2}kP \times \left({10}^{- 3} - {10}^{- 6}\right){m}^{3}

=2.25kJ−0.1kJ= 2 . 25kJ - 0 . 1kJ

=2.15kJ= 2 . 15kJ

Therefore, I-P

(II)

For isobaric process,

V1V2=T1T2⇒T2=3×500=1500K\dfrac{{V}_{1}}{{V}_{2}} = \dfrac{{T}_{1}}{{T}_{2}} ⇒ {T}_{2} = 3 \times 500 = 1500K

Now the change in the internal energy will be,

∆U=nCV∆T=0.2×52×8×1000=4kJ∆ U = n{C}_{V} ∆ T = 0 . 2 \times \dfrac{5}{2} \times 8 \times 1000 = 4kJ

Therefore, II-R

(III) 

For adiabatic expansion of monoatomic gas (γ=53)\left(\gamma = \dfrac{5}{3}\right)

P1V1γ=P2V2γ⇒(2kPa)×V053=P2×(V08)53{P}_{1}{V}_{1}^{\gamma} = {P}_{2}{V}_{2}^{\gamma} ⇒ \left(2kPa\right) \times {V}_{0}^{\dfrac{5}{3}} = {P}_{2} \times \left(\dfrac{{V}_{0}}{8}\right)\dfrac{5}{3}

⇒P2=64kPa⇒ {P}_{2} = 64kPa

Now the change in the internal energy will be,

\DeltaU=nCv\DeltaT\DeltaU = n{C}_{v}\DeltaT

=3nR\DeltaT2=32(P2V2−P1V1)=32×(64×13×8−2×13)= \dfrac{3nR\DeltaT}{2} = \dfrac{3}{2}\left({P}_{2}{V}_{2} - {P}_{1}{V}_{1}\right) = \dfrac{3}{2} \times \left(64 \times \dfrac{1}{3 \times 8} - 2 \times \dfrac{1}{3}\right)

=32×(83−23)=3kJ= \dfrac{3}{2} \times \left(\dfrac{8}{3} - \dfrac{2}{3}\right) = 3kJ

Therefore, III-T

(IV)

For diatomic gas whose molecules vibrate,

CV=62R{C}_{V} = \dfrac{6}{2}R and CP=82R{C}_{P} = \dfrac{8}{2}R

⇒\DeltaU=nCV\DeltaT=3nR\DeltaT⇒ \DeltaU = n{C}_{V}\DeltaT = 3nR\DeltaT

\DeltaQ=nCp\DeltaT=4nR\DeltaT\DeltaQ = n{C}_{p}\DeltaT = 4nR\DeltaT

\DeltaU\DeltaQ=34\dfrac{\DeltaU}{\DeltaQ} = \dfrac{3}{4}

\DeltaU=34×9=6.75≃7kJ\DeltaU = \dfrac{3}{4} \times 9 = 6 . 75 ≃ 7kJ

Therefore, IV-Q

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