First Law of Thermodynamics Part II

1. First Law of ThermodynamicsPart II Contributions by: John L. Falconer & Will MedlinDepartment of Chemical and Biological EngineeringUniversity of ColoradoBoulder, 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 __________________. increases decreases does not change Need more information Stopper Vacuum Block 1 kg Piston Gas

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 B C All have the same final temperature Vacuum Vacuum Vacuum 2 kg A C B 1 kg Block Piston Gas Gas Gas

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 B C All have the same final temperature B C A 2 kg 1 kg Block Piston Stopper Gas Gas Gas

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

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? yes  no need more information   Air 70°F 1 atm Stopper 2 kg Weight Piston Air 70°F 5 atm

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 _____________. increases   remains the same   decreases   Stopper 1 kg Weight Piston Air High P

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 B Both systems have the same final temperature Need more information. Gas 1 bar Gas 1 bar A B Isothermal Adiabatic

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 ____________. to the air inside the cylinder. from the air inside the cylinder. nowhere. No heat transfer takes place. Air 70°F 1 atm Stopper Weight 1 kg Piston Air 70°F 5 atm

10. 1 kg Weight 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 ____________. to the air from the air nowhere. No heat transfer takes place. Need more information. Stopper Piston Air 70°F 1 atm

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 _________. increases decreases remains the same Stoppers 10 MPa 300°C gas Diaphragm Vacuum

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 _________. increases decreases remains the same 10 MPa 10 MPa 300°C gas Diaphragm Vacuum

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 _________. increases decreases remains the same 10 MPa 10 MPa 300°C gas Diaphragm Vacuum

14. What must be changed about the First Law for a system with a chemical reaction? Add equilibrium term Add heat of reaction term 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 __________ pure A is fed to the rector a mixture of A and inert is fed to the reactor in neither case

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 __________. increases decreases remains the same

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

18. An endothermic reaction takes place in continuous-flow, isothermal reactor. The enthalpy of the effluent is ___________ the inlet enthalpy. higher than lower than 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. decreases remains constant increases 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 ________. increases decreases remains the same 500 Isenthalp T (°R) 450 Joule-Thomson inversion curve 400 0 5,000 10,000 P (psia)

21. A saturated vapor is fed to a turbine: The exit from the turbine is ______________. saturated vapor superheated vapor a vapor-liquid mixture P1 P2 sat. vapor W

22. High pressure liquid enters a throttle. What is true about the composition at the outlet? It is all liquid It is all vapor It is a mixture of liquid and vapor 5 MPa 200°C H2O(l) 0.1 MPa T = ? Valve

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

24. 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. lower higher same

25. The temperature at the exit of a reversible turbine will be ________ than the entrance. higher lower the same as

26. A membrane divides a rigid, well-insulated 2 m3 tank into equal parts. The left side contains an ideal gas (Cp= 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? 200 K 300 K 400 K Need more information Vacuum Gas Membrane

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

28. 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. greater than less than equal to