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Concepts Of Physics MCQ Edition [Volume 2]
Exam
Concepts Of Physics MCQ Edition [Volume 2]
Subject
Physics
Chapter
Specific Heat Capacities of Gases

Concepts Of Physics MCQ Edition [Volume 2] · Physics · Specific Heat Capacities of Gases

Half mole of an ideal gas ( γ = 5/3 ) is taken through a cycle...

Half mole of an ideal gas (γ=5/3\gamma = 5/3) is taken through a cycle abcdaabcda in a PP-VV diagram. The states are located at a(5000 cm3,100 kPa)a(5000 \text{ cm}^3, 100 \text{ kPa}), b(10000 cm3,100 kPa)b(10000 \text{ cm}^3, 100 \text{ kPa}), c(10000 cm3,200 kPa)c(10000 \text{ cm}^3, 200 \text{ kPa}), and d(5000 cm3,200 kPa)d(5000 \text{ cm}^3, 200 \text{ kPa}). Take R=253 J K−1 mol−1R = \dfrac{25}{3} \text{ J K}^{-1} \text{ mol}^{-1}. Determine the amount of heat liberated in the processes cdcd and dada.
Half mole of an ideal gas ( γ = 5/3 ) is taken through a cycle abcda in a P - V diagram. The states are located at

Options

  1. A750 J750 \text{ J}, 2500 J2500 \text{ J}
  2. B1000 J1000 \text{ J}, 500 J500 \text{ J}
  3. C2500 J2500 \text{ J}, 750 J750 \text{ J}
  4. D1500 J1500 \text{ J}, 1250 J1250 \text{ J}

Correct answer

C. 2500 J2500 \text{ J}, 750 J750 \text{ J}

Step-by-step solution

Given γ=53\gamma = \dfrac{5}{3}, the molar heat capacities are Cv=Rγ−1=32RC_v = \dfrac{R}{\gamma - 1} = \dfrac{3}{2}R and Cp=Cv+R=52RC_p = C_v + R = \dfrac{5}{2}R.

For the isobaric process cdcd, the pressure is constant at P=200 kPa=2×105 PaP = 200 \text{ kPa} = 2 \times 10^5 \text{ Pa}.

The heat exchanged is Qcd=nCpΔT=CpRPΔV=52P(Vd−Vc)Q_{cd} = n C_p \Delta T = \dfrac{C_p}{R} P \Delta V = \dfrac{5}{2} P (V_d - V_c).

Substituting the given values:

Qcd=52×(2×105)×(5000−10000)×10−6=−2500 JQ_{cd} = \dfrac{5}{2} \times (2 \times 10^5) \times (5000 - 10000) \times 10^{-6} = -2500 \text{ J}.

The negative sign indicates that 2500 J2500 \text{ J} of heat is liberated.

For the isochoric process dada, the volume is constant at V=5000 cm3=5×10−3 m3V = 5000 \text{ cm}^3 = 5 \times 10^{-3} \text{ m}^3.

The heat exchanged is Qda=nCvΔT=CvRVΔP=32V(Pa−Pd)Q_{da} = n C_v \Delta T = \dfrac{C_v}{R} V \Delta P = \dfrac{3}{2} V (P_a - P_d).

Substituting the given values:

Qda=32×(5×10−3)×(100−200)×103=−750 JQ_{da} = \dfrac{3}{2} \times (5 \times 10^{-3}) \times (100 - 200) \times 10^3 = -750 \text{ J}.

The negative sign indicates that 750 J750 \text{ J} of heat is liberated.

Thus, the heat liberated in processes cdcd and dada are 2500 J2500 \text{ J} and 750 J750 \text{ J} respectively.

Answer: 2500 J2500 \text{ J}, 750 J750 \text{ J}
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