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First Law of Thermodynamics Part 2 Contributions by: John L. Falconer & Will Medlin Department of Chemical and Biological Engineering University of Colorado.

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Presentation on theme: "First Law of Thermodynamics Part 2 Contributions by: John L. Falconer & Will Medlin Department of Chemical and Biological Engineering University of Colorado."— Presentation transcript:

1 First Law of Thermodynamics Part 2 Contributions by: John L. Falconer & Will Medlin Department of Chemical and Biological Engineering University of Colorado Boulder, CO 80309-0424 Supported by the National Science Foundation

2 An ideal gas is at 1 atm in a piston-cylinder. The piston is weightless and frictionless. When the mass is removed from the piston, the gas temperature __________________. A.increases B.decreases C.does not change D.Need more information 1 kg Vacuum Gas Piston Block Stopper

3 In these piston-cylinder systems, when the red stop is removed, the ideal gas expands, and the piston moves until it hits the black stopper. Each system is adiabatic and starts at 10 atm and 25°C. Which has the highest final temperature? A.A B.B C.C D.All have the same final temperature 3 2 kg Vacuum Gas Piston Block A 1 kg Vacuum Gas B Vacuum Gas C

4 In these piston-cylinders, when the red stops are removed, the gases are compressed, and the pistons move until they hit the black stopper. Each system is adiabatic, and each starts at the same temperature and pressure. Which has the highest final temperature? A.A B.B C.C D.All have the same final temperature 4 2 kg Gas Piston Block Stopper A 1 kg Gas B C

5 A gas is heated and expands in a sealed, frictionless, piston-cylinder arrangement. In this process, work is ________________. A.done on the gas B.done by the gas C.not done D.Need more information. 1 kg Gas Heat 1 kg Gas

6 Air in a piston-cylinder device is initially at 70°F and 5 atm in surroundings that are at 70°F, 1 atm. If the locks holding the piston in place are removed, the piston moves to the stopper, and the air pressure changes to 2 atm while temperature remains constant. Frictional effects are negligible. Is there heat transfer involved in this process? A.yes B.no C.need more information 2 kg Air 70°F 5 atm Piston Weight Air 70°F 1 atm Stopper

7 Air at high pressure and ambient temperature is contained in a perfectly insulated piston-cylinder device. If the locks holding the piston in place are removed, the piston moves upwards to a stopper. The temperature of the air _____________. A.increases B.remains the same C.decreases 1 kg Air High P Piston Weight Stopper

8 Two different systems, isothermal (A) & adiabatic (B), contain ideal gases in piston-cylinders at the same temperature and pressure. If you compress both systems to 10 bar, which system has the higher temperature at the end of the compression? A.A B.B C.Both systems have the same final temperature D.Need more information. Gas 1 bar Gas 1 bar AB IsothermalAdiabatic

9 Air in a piston-cylinder is at 70°F and 5 atm. The piston is locked in place. The locks are removed, and the piston moves to a stopper where the air is now at 70°F and 2 atm. Heat is transferred ____________. A.to the air inside the cylinder. B.from the air inside the cylinder. C.nowhere. No heat transfer takes place. 1 kg Air 70°F 5 atm Piston Weight Air 70°F 1 atm Stopper

10 Air in a piston-cylinder is at 70°F and 1 atm. A weight is added to the piston, and the air increases to 4 atm at 70°F. Heat is transferred ____________. A.to the air B.from the air C.nowhere. No heat transfer takes place. D.Need more information. 1 kg Air 70°F 1 atm Piston Weight Stopper

11 Stoppers prevents a piston from moving within a piston-cylinder system. When the diaphragm is removed from this piston-cylinder system, the energy of the gas _________. A.increases B.decreases C.remains the same Vacuum Diaphragm 10 MPa 300°C gas Stoppers

12 A piston pushing on a gas holds it at a pressure of 10 MPa. When the diaphragm is removed from this piston-cylinder system, the energy of the gas _________. A.increases B.decreases C.remains the same Vacuum Diaphragm 10 MPa 300°C gas 10 MPa

13 A piston pushing on a gas holds it at a pressure of 10 MPa. When the diaphragm is removed from this piston-cylinder system, the temperature of the gas _________. A.increases B.decreases C.remains the same Vacuum Diaphragm 10 MPa 300°C gas 10 MPa

14 What must be changed about the First Law for a system with a chemical reaction? A.Add equilibrium term B.Add heat of reaction term C.Don’t change anything

15 An endothermic reaction takes place in an adiabatic reactor. The reaction (A  B) goes to completion. The effluent temperature is higher when __________ A.pure A is fed to the rector B.a mixture of A and inert is fed to the reactor C.in neither case 15

16 An endothermic reaction takes place in an adiabatic reactor and the conversion is 100%. If the inlet flow rate is decreased by a factor of two, and the conversion remains at 100%, then the exit temperature __________. A.increases B.decreases C.remains the same 16

17 An endothermic reaction takes place in continuous- flow, adiabatic reactor. The enthalpy of the effluent is __________ the inlet enthalpy. A.higher than B.lower than C.the same as

18 An endothermic reaction takes place in continuous- flow, isothermal reactor. The enthalpy of the effluent is ___________ the inlet enthalpy. A.higher than B.lower than C.the same as

19 A can of office duster (used for cleaning cameras and keyboards) contains a liquid-vapor mixture of 1,1,1,2- tetrafluoroethane. If the container is used continuously by depressing the nozzle, the flow rate of air ____________ with time. A.decreases B.remains constant C.increases D.remains constant and then decreases

20 Methane undergoes a rapid expansion through an insulated valve. The starting pressure is 5,000 psia and the starting temperature is 475°R. The temperature ________. A.increases B.decreases C.remains the same T (°R) P (psia) 500 450 400 05,00010,000 Isenthalp Joule-Thomson inversion curve

21 A saturated vapor is fed to a turbine: The exit from the turbine is ______________. A.saturated vapor B.superheated vapor C.a vapor-liquid mixture P1P1 sat. vapor P2P2 W

22 High pressure liquid enters a throttle. What is true about the composition at the outlet? A.It is all liquid B.It is all vapor C.It is a mixture of liquid and vapor 5 MPa 200°C H 2 O (l) 0.1 MPa T = ? Valve

23 An ideal gas expands through a throttle process: Is the outlet temperature... A.> 350 K B.< 350 K C.= 350 K D.Need more information 1 MPa 350 K Gas 0.1 MPa Gas T = ? Throttle

24 Liquid water at 175°C and 20 bar is fed to a throttle: The outlet pressure is 1 bar. What is the most likely outlet temperature? Assume one of the following is correct. A.175°C B.150°C C.100°C D.50°C 20 bar 175 ° C Liquid 1 bar T = ? Throttle

25 Steam at 150°C and 2 bar is expanded to 1 bar in turbine. The turbine has an efficiency of 40%. The quality of the steam will be ________ compared to a turbine with 100% efficiency. A.lower B.higher C.same

26 The temperature at the exit of a reversible turbine will be ________ than the entrance. A.higher B.lower C.the same as

27 A membrane divides a rigid, well-insulated 2 m 3 tank into equal parts. The left side contains an ideal gas (C p = 30 J/mol K) at 300 K and 10 bar and the right side is a vacuum. If the membrane ruptures, what will be the final temperature of the gas? A.200 K B.300 K C.400 K D.Need more information Gas Vacuum Membrane

28 What would cause the temperature of an ideal gas in a closed system (similar to the membrane system below) to change? A.Work is done by the gas. B.Interactions between molecules change. C.Gas occupies more volume when the membrane ruptures. D.None of the above. Gas Vacuum Membrane

29 A liquid mixture at 20 bar is fed to an adiabatic throttle that is also a catalyst. The exit from the throttle is a gas at 1 bar and has 50% of the feed converted to reaction products. If the reaction is exothermic, the enthalpy of the exit stream is __________ the enthalpy of the feed. A.greater than B.less than C.equal to


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