First Law of Thermodynamics
Contributions by:John L. Falconer & Will Medlin
Department of Chemical and Biological EngineeringUniversity of Colorado
Boulder, CO 80309-0424
Supported by the National Science Foundation
When a hydrogen molecule dissociates into two H atoms, energy is ______________.
A. added
B. removed
C. neither added nor removed
H H
HH
Consider a completely insulated, closed system of fixed volume. The exothermic thermite reaction takes place in the system. The system energy __________.
A. increases
B. decreases
C. stays the same
D. need more information
System
Insulation Insulation
System
An endothermic reaction takes place in a completely insulated, closed container of fixed volume. The internal energy of the container _____________.
A. increases
B. decreases
C. stays the same
D. Need more information
System
Insulation Insulation
Container
An endothermic reaction takes place in an isothermal, closed container of fixed volume. The internal energy of the container ____________.
A. increases
B. decreases
C. stays the same
5
An exothermic reaction takes place in an isothermal, closed container of fixed volume. The internal energy of the container _____________.
A. increases
B. decreases
C. stays the same
D. Need more information
6
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.
A. higher than
B. lower than
C. the same as
7
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.
A. higher than
B. lower than
C. the same as
8
An endothermic reaction takes place in a continuous-flow, adiabatic reactor. The enthalpy of the effluent is ____________ the enthalpy of the inlet.
A. higher than
B. lower than
C. the same as
9
An exothermic reaction takes place in a continuous-flow, adiabatic reactor. The enthalpy of the effluent is _____________ the enthalpy of the inlet.
A. higher than
B. lower than
C. the same as
10
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 ___________.
A. increases
B. decreases
C. does not change
11
BLACKBOX
Weight slowly drawn up to box
Very thinthread
TABLE
Completely isolated (except for thread)
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 ______________.
A. 500°C
B. 600°C
C. 700°C
D. Need more information
Pre-Heater Reactor
Reactor
100oC
100oC 500oCX=0.7
T = ?X=0.7
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 _____________.
A. increases
B. decreases
C. remains the same
D. Need more information
A B A 10 mol/hr X = 1.0
T = 400oC
A B A 20 mol/hr X = 1.0
T = ?
10 mol/hrInert
10 mol/hrInert
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.
A. higher than
B. lower than
C. equal to
A C AB
10 mol/hr X = 1.0
T = 60oC
A C AB
20 mol/hr X = 0.75
T = ?
What is the equation for work for steady-state flow?
A. -PDV
B. -D(PV)
C. -VDP
D. None of the above
gas flow
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?
A. Process A
B. Process B
1 2
1 2
50 kJ
200 kJ
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. A constant pressure process to the final volume and then constant volume to 5 bar.
B. A constant volume process to 5 bar and then constant pressure to the final volume.
C. Same work for both
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.
A. greater than
B. less than
C. equal to
D. Need more information
Container
CH4
120°C15 bar
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.
A. greater than
B. less than
C. equal to
D. Need more information
CH4
120°C & 2 bar
CH4
120°C15 bar
Two reversible pathways are shown. Which one has the larger value of Q?
A. 1 2 3 1
B. 1 4 5 1
C. Both have the same Q
D. Q is zero for both pathways
An electric fan is turned on in a room with all the doors closed. The room temperature ___________.
A. increases
B. decreases
C. remains the same
D. Need more information
21
A battery-operated fan is turned on in a room with all the doors closed. The room temperature ______________.
A. increases
B. decreases
C. remains the same
D. Need more information.
22
A battery-operated fan is turned on in a room with all the doors closed. The energy in the room ______________.
A. increases
B. decreases
C. remains the same
D. Need more information
23
A refrigerator door is opened in a kitchen and all the doors to the kitchen are closed. The kitchen temperature ______________.
A. increases
B. decreases
C. remains the same
24
An ideal gas is compressed to 10 times its initial pressure. The final volume is smaller for _________.
A. an isothermal compression
B. an adiabatic reversible compression
C. neither. It is the same in both.
Which substance at 25°C requires the most work per kg to compress from 1 bar to 25 bar?
A. Water
B. Hexane
C. Mercury
D. Air
E. Same work for all
26
Which of the following, when fed with an organic to an oxidation reaction, has the higher adiabatic temperature?
A. A stoichiometric amount of pure O2
B. 50% excess oxygen (pure)
C. A stoichiometric amount of air
For which system is the value of the internal energy the highest?
A. One kg of steam
B. One kg of liquid water
C. Both systems have the same internal energy
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 _____________.
A. increases
B. remains the same
C. decreases H2O
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 ___________.
A. increases
B. decreases
C. does not change
Gas20°C1 atm
Start After heating
Gas250°C
