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First Law of Thermodynamics

First Law of Thermodynamics. 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.

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First Law of Thermodynamics

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  1. First Law of Thermodynamics Contributions by: John L. Falconer & Will MedlinDepartment of Chemical and Biological EngineeringUniversity of ColoradoBoulder, CO 80309-0424 Supported by the National Science Foundation

  2. When a hydrogen molecule dissociates into two H atoms, energy is ______________. added removed neither added nor removed H H H H

  3. Insulation System Consider a completely insulated, closed system of fixed volume. The exothermic thermite reaction takes place in the system. The system energy __________. increases decreases stays the same need more information

  4. Insulation Container An endothermic reaction takes place in a completely insulated, closed container of fixed volume. The internal energy of the container _____________. increases decreases stays the same Need more information

  5. An endothermic reaction takes place in an isothermal, closed container of fixed volume. The internal energy of the container ____________. increases decreases stays the same

  6. An exothermic reaction takes place in an isothermal, closed container of fixed volume. The internal energy of the container _____________. increases decreases stays the same Need more information

  7. An endothermic reaction takes place in a continuous-flow, isothermal reactor at constant pressure. The enthalpy of the effluent is _________________ the enthalpy of the inlet. higher than lower than the same as

  8. An exothermic reaction takes place in a continuous-flow, isothermal reactor at constant pressure. The enthalpy of the effluent is ____________ the enthalpy of the inlet. higher than lower than the same as

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

  10. An exothermic reaction takes place in a continuous-flow, adiabatic reactor. The enthalpy of the effluent is _____________ the enthalpy of the inlet. higher than lower than the same as

  11. Completely isolated (except for thread) A weight hangs by a thin thread from a black box that is completely isolated from the surroundings. The weight slowly rises. The energy of the box ___________. increases decreases does not change BLACK BOX TABLE Very thin thread Weight slowly drawn up to box

  12. Two adiabatic reactor setups contain the same reaction with 70% conversion at steady state. The preheater heats the feed stream and causes a 200°C decrease in the reactor effluent. Assume perfect heat exchangers. The exit temperature of the system with the preheater is ______________. 500°C 600°C 700°C Need more information 100oC 500oC X=0.7 Reactor T = ? X=0.7 100oC Reactor Pre-Heater

  13. A steady state, adiabatic reactor is fed a mixture of A and an inert; the flow rate of each is 10 mol/hr. The exothermic reaction A  B goes to completion. The outlet temperature is 400oC. When the flow rate of A is increased to 20 mol/hr while the inert remains at 10 mol/hr, conversion is still complete and the effluent temperature _____________. increases decreases remains the same Need more information X = 1.0 T = 400oC 10 mol/hr A A  B Inert 10 mol/hr X = 1.0 T = ? 20 mol/hr A A  B Inert 10 mol/hr

  14. An endothermic reaction (A  C) takes place in an adiabatic flow reactor. The feed is a 50/50 mixture of reactant A and inert B. At a flow rate of 10 mol/hr, conversion of A is 100% and the outlet temperature is 60oC. The feed flow rate is doubled, and only 75% of A is converted to C. The outlet temperature is _____________ 60oC. higher than lower than equal to X = 1.0 T = 60oC 10 mol/hr A B A  C X = 0.75 T = ? 20 mol/hr A B A  C

  15. gas flow -PDV -D(PV) -VDP None of the above What is the equation for work for steady-state flow?

  16. An ideal gas goes from state 1 to 2 by two processes. Process A is reversible and has 50 kJ of work done on the gas. Process B is irreversible and has 200 kJ of work done on the gas. If one process requires heat to be added and the other removed, which process has to have heat added? Process A Process B 50 kJ 1 2 200 kJ 1 2

  17. A gas undergoes reversible expansion from 40 barand 500 K to 5 bar and 500 K by two pathways. Which process creates more |work|? A constant pressure process to the final volume and then constant volume to 5 bar. A constant volume process to 5 bar and then constant pressure to the final volume. Same work for both

  18. Methane at 15 bar and 120°C flows into an evacuated container when the valve is open. When the pressure in the container reaches 15 bar, the temperature of the methane is _______ 120°C. greater than less than equal to Need more information CH4 120°C 15 bar Container

  19. Methane at 15 bar and 120°C flows into a container that has methane at 120°C and 2 bar when the valve is opened. When the pressure in the container reaches 15 bar, the temperature of the methane in the container is ___________ 120°C. greater than less than equal to Need more information CH4 CH4 120°C & 2 bar 120°C 15 bar

  20. Two reversible pathways are shown. Which one has the larger value of Q? 1  2  3  1 1  4  5  1 Both have the same Q Q is zero for both pathways

  21. An electric fan is turned on in a room with all the doors closed. The room temperature ___________. increases decreases remains the same Need more information

  22. A battery-operated fan is turned on in a room with all the doors closed. The room temperature ______________. increases decreases remains the same Need more information.

  23. A battery-operated fan is turned on in a room with all the doors closed. The energy in the room ______________. increases decreases remains the same Need more information

  24. A refrigerator door is opened in a kitchen and all the doors to the kitchen are closed. The kitchen temperature ______________. increases decreases remains the same

  25. An ideal gas is compressed to 10 times its initial pressure. The final volume is smaller for _________. an isothermal compression an adiabatic reversible compression neither. It is the same in both.

  26. Which substance at 25°C requires the most work per kg to compress from 1 bar to 25 bar? Water Hexane Mercury Air Same work for all

  27. Which of the following, when fed with an organic to an oxidation reaction, has the higher adiabatic temperature? A stoichiometric amount of pure O2 50% excess oxygen (pure) A stoichiometric amount of air

  28. For which system is the value of the internal energy the highest? One kg of steam One kg of liquid water Both systems have the same internal energy

  29. A pot of water is boiling open to the atmosphere when the pot is sealed by a tight lid, and continued heating causes the pressure to rise. Compared to before the lid was added, the temperature _____________. increases   remains the same   decreases   H2O

  30. Air is contained in a sealed tank of fixed volume. The air in the tank is initially at 20°C and 1 atm. It is then heated to 250°C. The energy of the air in the container ___________. increases  decreases does not change   Gas 250°C Gas 20°C 1 atm Start After heating

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