Ask Question
24 May, 07:30

A piston-cylinder assembly contains 5 kg of air, initially at 2.0 bar, 30 C. The air undergoes a process to a state where the pressure is 2 bar, during which the pressure-volume relationship is pV1.5 = constant. Assume ideal gas behavior for the air. Determine the work and heat transfer, in kJ. Note molar mass of air is 28.96 g/mole

+2
Answers (1)
  1. 24 May, 10:44
    0
    Answer: wor done is 145. 06kJ

    Heat transfer is 135.53kJ

    Explanation:

    No of moles of air = mass/molar mass = 5000g/28gmol^-1 = 172.65mol

    P1 = 2bar = 2*101300 = 202600pa

    T1 = 30° + 273k = 303k

    P2 = p1 = 202600pa

    V2 = ? T2 = ?

    Using pV = nRT

    R = 8.314 PA m^3 mol^-1 k^-1

    V1 = (172.65*8.314*303) / 202600

    V1 = 2.146m^3

    For second state, 1.5pv = const = P1V1

    V2 = (202600*2.146) / (1.5*202600)

    V2 = 1.43m^3

    Volume change = 2.146 - 1.43 = 0.715m^3

    Word done = pressure * volume change

    W = 202600*0.716 = 145061.6J

    = 145.061kJ

    Using V1/T1 = V2/T2

    T2 = V2T1/V1

    = (1.43*303) / 2.146 = 201.9k

    For internal energy U

    U = nCv * (T2 - T1)

    *CV is the heat capacity at const. vol approximately 0.718J mol^-1 k^-1

    U = 172.65*0.718 * (201.9-303)

    U = - 12532.6J = - 12.532kJ

    The - ve means the system lost internal energy.

    Q = U+W = total heat energy of system

    Q = - 12.532+145.061 = 132.52 kJ
Know the Answer?
Not Sure About the Answer?
Find an answer to your question ✅ “A piston-cylinder assembly contains 5 kg of air, initially at 2.0 bar, 30 C. The air undergoes a process to a state where the pressure is 2 ...” in 📘 Engineering if you're in doubt about the correctness of the answers or there's no answer, then try to use the smart search and find answers to the similar questions.
Search for Other Answers