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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

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

slide2
An unknown compound is at 200°C and 1 MPa. How many phases could be present?

1

2

1 or 2

3

Not possible to specify both temperature and pressure

slide3
A mixture of ethanol and propanol are at 60°C. Both liquid and vapor are present. How many additional variables can be specified before the system is completely determined?

0

1

2

3

System is already over-specified

slide4
A mixture of ethanol and propanol are at 60°C. Both liquid and vapor are present. The pressure is 1 bar. How many additional variables can be specified before the system is completely determined?

0

1

2

3

System is already over-specified

slide5
A mixture of ethanol and propanol are at 60°C. Both liquid and vapor are present. The pressure is 1 bar and the liquid mole fraction of ethanol is 0.5. How many additional variables can be specified before the system is completely determined?

0

1

2

3

System is already over-specified

slide6
Which of the following is not possible:

2 components in VLE equilibrium, both temperature and pressure are specified.

1 component in three phases: solid, liquid, gas.

2 solids in equilibrium at a specified temperature.

2 components as solid and liquid, with temperature, pressure, and mole fractions specified.

1 component as a gas, temperature and mole fractions specified.

slide7
When a hydrogen molecule dissociates into two H atoms, energy is ______________.

added

removed

neither added nor removed

H

H

H

H

slide8

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

slide9

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

slide10
An endothermic reaction takes place in an isothermal, closed container of fixed volume.

The internal energy of the container ____________.

increases

decreases

stays the same

slide11
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

slide12
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

slide13
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

slide14
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

slide15
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

slide16

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

slide17
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

slide18
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

slide19
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

slide20

gas flow

-PDV

-D(PV)

-VDP

None of the above

What is the equation for work for steady-state flow?

slide21
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

slide22
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

slide23
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

slide24
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

slide25
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

slide26
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

slide27
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.

slide28
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

slide29
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

slide30
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.

slide31
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

slide32
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

slide33
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

slide34
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

slide35
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