Engineering Board Exam Reviewer · Thermodynamics · hard

A 0.5 m3 rigid tank contains air at 400 kPa and 300 K. The tank is heated and a relief valve releases air so that the remaining air is at 400 kPa and 350 K. How much air left the tank? (R = 0.287 kJ/kg· K)

  1. 0.332 kg
  2. 2.323 kg
  3. 1.991 kg
  4. 0.000 kg

Answer

A. 0.332 kg

Solution

m1 = PV/RT1 = 400(0.5)/[0.287(300)] = 2.323 kg; m2 = 400(0.5)/[0.287(350)] = 1.991 kg. m = 0.332 kg.

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  2. Air consists of approximately 79% N2 and 21% O2 by mole. What is its apparent molecular weight? (M N2 = 28, M O2 = 32)
  3. How many kilomoles are there in 5 kg of carbon dioxide (M = 44 kg/kmol)?
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  5. A gas has a specific gas constant of 0.2598 kJ/kg· K. What is its molecular weight?
  6. What is the specific gas constant of a gas with a molecular weight of 28 kg/kmol (e.g., nitrogen)?
  7. A gas in a rigid container is at 200 kPa and 300 K. If it is heated to 450 K, what is its final pressure?
  8. A gas occupies 2 m3 at 300 K. If it is heated at constant pressure to 450 K, what is its final volume?
  9. A gas occupies 3 m3 at 100 kPa. If it is compressed isothermally to 1 m3, what is its final pressure?
  10. What is the mass of air in a 2 m3 tank at 500 kPa absolute and 300 K? (R = 0.287 kJ/kg· K)

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