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Unformatted text preview: 4200:225 EQUILIBRIUM THERMODYNAMICS SPRING 90 TEST 1 SSN________ 1. Short Answer a) Estimate the change in entropy when one mole of nitrogen is compressed by a piston in a cylinder from 300K and 23 liters/gmol to 400K and 460 liters/gmol.(Cp=7 cal/gmol) b) Draw a sketch of the square well potential and indicate the position(s) where the force between two atoms is zero. c) Write the simplest possible form of the energy balance for application to the following process and system: water drips slowly out of a hole in the bottom of an enclosed tank; system: the tank and its contents. d) Write the simplest possible form of the energy balance for application to the following process and system: a rubber balloon being inflated; system: the balloon and its contents. 2. Estimate the density (g/cc) of liquid butane at 300 K and 38 psia. Assuming that a disposable lighter costs $1.00 and contains 2 g of butane, what is the value of the butane? ($/gal) 3. Saturated steam at 660 F is adiabatically throttled to atmospheric pressure. Estimate the final condition of the steam. 4. A mixture of 1CO:2H2 is adiabatically continuously compressed from 5 atm and 100 F to 100 atm and 1100 F. Estimate the work of compressing 1 ton of the gas.(Cp=7Btu/lbmol-R) 5. Determine the efficiency of the compressor in problem 4. 6. An insulated cylinder is fitted with a freely floating piston and contains 1 lbm of steam at 120 psia and 90% quality. The space above the piston, initially 1 ft 3 , contains air at 300 K to maintain the pressure on the steam. Additional air is forced into the upper chamber, forcing the piston down and increasing the steam pressure until the steam has 100% quality. The final steam pressure is 428 psia and the work done on the steam is 91 Btu, but the air above the steam has not had time to exchange heat with the piston, cylinder or surroundings. The air supply line is at 700 psia and 300 K. What is the final temperature of the air in the upper chamber? 1a)7.4cal/mol-K (c)HdM=d(MU) (d)HdM+W=d(MU) 2).6 g/cc 3) 0.96 4) 1.3E6 5) 76% 6)360K 4200:225 EQUILIBRIUM THERMODYNAMICS SPRING 91 TEST 1 SSN________ 1. Short Answer a) 15 molecules are distributed as 9:4:2 between boxes A:B:C respectively. The partitions between the boxes are removed and the molecules distribute themselves evenly between the boxes. Compute S. b) Explain in words how the pressure of a fluid against the walls of its container is related to the velocity of the molecules. c) What is it about molecules that requires us to add heat to convert liquids to gases? d) A rigid cylinder of gaseous hydrogen is heated from 300K and 1 bar to 400K. How much heat is added to the gas? 2. Steam is produced at 30 bar and some unknown temperature. A small amount of steam is bled off and goes through an adiabatic throttling valve to 1 bar. The temperature of the steam exiting the throttling valve is 110 C....
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