Thermodynamics - Questions from First Law

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  1. 10 kg of water is stirred in an agitator with a 2 HP motor. Heat is added at the rate of 1 kW. Find the change in internal energy.
  2. 2 kg of air at 10 atm and 300oC is allowed to expand adiabatically to 5 times its original volume. Find the final volume, the work done and change in internal energy. CV = 0.1714 kcal/kg.oC
  3. An insulated and non-conducting container filled with 10 kg of water at 20oC is fitted with a stirrer, which is made to turn by lowering a weight of 25 kg mass. The weight slowly falls a distance 10 meters while turning the stirrer. Assuming that all the work done by gravity is transferred to water, determine the internal energy change of water, and the final temperature.
  4. Air is compressed from 2 atm absolute and 28oC to 6 atm absolute and 28oC by heating at constant volume followed by cooling at constant pressure. Calculate the heat and work requirements and DE and DH of the air.
  5. Water at 93.3oC is being pumped from a storage tank at a rate of 198.24 litres/min by a pump. The motor deriving the pump supplies energy at the rate of 2 HP. The water passes through a heat exchanger where it gives up heat at the rate of 1,68,000 cal/sec and is delivered to a second storage tank at an elevation of 15.24 meters above the first tank. What is the temperature of the water delivered to the second tank? Density of water at 93.3oC = 60.1 lb/ft3; specific heat of water = 1
  6. Calculate Q, W, DU and DH for the following:
  7. Gas: Ideal, 2kmol
    Initial conditions: 2 atm, 20 m3, 300 K
    Final conditions: 10 atm, 2 m3, 300 K

    1. Isothermal compression
    2. Isometric followed by isobaric process.

  8. Water is pumped from a tank to a overhead tank 15 meters above using a 2 HP pump. The water rate is 100 kg/min. What is the change in enthalpy of the process?
  9. 220 kg of CO2 gas at 27oC and 1 atm is compressed adiabatically to 1/5th of its volume. It is then cooled to its original temperature. Find DQ, DU and W for each step and for the entire process.


M.Subramanian, Lecturer, Chemical Engg, SVCE, Sriperumbudur - 602105, Tamil Nadu, INDIA