Reversible & Irreversible

ProcessesContributions by:

John L. FalconerDepartment of Chemical and Biological Engineering

University of ColoradoBoulder, CO 80309-0424

Supported by the National Science Foundation

When the red stops are removed, the ideal gases expand, and the pistons move until they hit the black stoppers. Each system is adiabatic.Which system has the most lost work?

A. A

B. B

C. C

D. Same for all systems

2

2 kg

Vacuum

Gas

A

1 kg

Vacuum

Gas

B

Vacuum

Gas

C

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 the same

3

2 kg

Vacuum

Gas

Piston

Block

A

1 kg

Vacuum

Gas

B

Vacuum

Gas

C

A pile of sand sits on a piston and the weight of the sand keeps the gas compressed in the cylinder. Which method to remove the sand expands the gas most reversibly?

A. All at once.

B. One grain at a time.

C. ¼th of the sand per minute.

D. Same for all methods

Gas

Piston

Sand

An ideal gas expands from 2 bar to 1 bar adiabatically but irreversibly. Compared to an adiabatic, reversible process from 2 bar to 1 bar, the final temperature will be _____________ for the irreversible process.

A. higher

B. lower

C. the same

The curve represents an adiabatic reversible process for an ideal gas. For any starting point on the line, which regions cannot be reached by an adiabatic irreversible process?

ABOVEU

V

U

V

BELOW

U

V

A B C

All regions can

be reached

Which of these processes could run under continuous, steady-state operation?

A. 1

B. 2 & 3

C. 3

D. 4

E. 1 & 4

W

Q

W

Q

W

Q

W

Q

#1 #2

#3 #4

Which of the following processes could run under continuous, steady-state operation?

A. 1

B. 2 & 3

C. 3

D. 4

E. 1 & 4

WQ

WQ

WQ

#2

#3 #4

#1

WQH

hot

coldQC

Which of the following processes could run under continuous, steady-state operation?

A. 1 & 2

B. 3 & 4

C. 3

D. 4

E. 1 & 3

WQH

hot

coldQC

#1W

QH

hot

coldQC

WQH

hot

coldQC

WQH

hot

coldQC

#2

#3 #4

Which of the following processes could run under continuous, steady-state operation?

A. 1

B. 3

C. 1 & 3

D. 4

E. 1 & 2

WQH

hot

coldQC

#1W

QH

hot

coldQC

WQH

hot

coldQC

WQH

hot

coldQC

#2

#3 #4

A gas goes from state A to state B in a reversible adiabatic process. It then goes from B back to A by a different pathway that is irreversible and not adiabatic. The entropy change for the gas for the irreversible pathway is _____________ zero.

A. greater than

B. less than

C. equal to

V

P

A

B

Rev.

Irrev.

A gas goes from state A to state B in a reversible adiabatic process. It then goes from B back to A by a different pathway that is irreversible and adiabatic so that the entropy change of the gas is zero. Is this possible?

A. Yes

B. No

C. Cannot tell

V

P

A

B

Rev.

Irrev.

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

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

12

3

4

5

P

V

Adiabatic expansions and compressions are shown for an ideal gas. One curve is reversible and one is irreversible in each figure. Which ones are the irreversible curves?

A. 1 & 3

B. 1 & 4

C. 2 & 3

D. 2 & 4

12P

T

start

34

P

Tstart

Each figure has three curves for a gas: (isothermal, reversible adiabatic, and irreversible adiabatic). Which curves are the irreversible adiabatic curves?

A. 1 & 4

B. 1 & 6

C. 3 & 4

D. 2 & 4

E. 3 & 6

start

P

V

1

3 2

start

P

V

4

5

6

The three curves represent isothermal, reversible adiabatic, and irreversible adiabatic processes for a gas. Which curve represents the irreversible adiabatic process?

A. 1

B. 2

C. 3

D. Cannot be determined

start

P

V

2

1

3

The three curves represent isothermal, reversible adiabatic, and irreversible adiabatic processes for a gas. Which curve represents the irreversible adiabatic process?

A. 1

B. 2

C. 3

D. Cannot be determined

start

P

V

1

3 2

An ideal gas goes from 10 atm and 50°C to 1 atm and 100°C by two pathways. Path A is reversible, it is a constant volume step followed by a constant pressure step. Path B is irreversible, and is a constant pressure step followed by a constant volume step. Which pathway has the larger entropy change for the gas?

A. A

B. B

C. They are the same

10 atm50°C

1 atm100°C

10 atm50°C

1 atm100°C

V P

P V

A

B

An inventor claims he can convert 1000 J of heat into 1000 J of work. Does this violate the second law?

A. Yes

B. Yes, if he claims to do it continuously

C. No

D. Cannot tell

Which process is the most irreversible?

A. Slowly increasing pressure on the gas phase reaction

2A(g) 2B(g)

B. Melting ice at 0°C by removing heat.

C. Slowly blowing up a balloon.

D. Slowly mixing 40°C water with 42°C water.

E. Boiling water in a piston/cylinder at 1 atm, 100°C.

Which process is closest to being reversible?

A. Slowly dissolving NaCl in water

B. Slowly burning carbon in O2 at 300°C

C. Slowly compressing a gas in a piston-cylinder so that the gas heats up

D. Expanding a gas through a nozzle to lower pressure

An ideal gas is compressed adiabatically and irreversibly. The final temperature of this process relative to that for an adiabatic reversible process to the same final pressure is ____________.

A. higher

B. lower

C. the same

The work for irreversible compression of an ideal gas in a piston-cylinder system is _______ the work for reversible compression.

A. higher than

B. lower than

C. the same as