APP2 PV Diagrams

For the process X→Y, ΔU is greater than zero and

• Q<0 and W = 0

• Q<0 and W>0

• Q>0 and W<0

• Q>0 and W=0

• Q>0 and W>0

Answer explanation

Process X- Y is isobaric. Constant pressure. The gas is also expanding (increasing volume). When the gas is expanding, the work done is negative. Heat is being added to the system to change the systems volume.

For the process Y→Z, Q is greater than zero and

• W<0 and ΔU=0

• W=0 and ΔU<0

• W=0 and ΔU>0

• W >0 and ΔU=0

• W>0 and ΔU>0

Answer explanation

Process Y-Z is isochoric. This means the volume remains constant. The pressure is increasing. There will be no work done because there is no change in volume. There will be an increase in temperature (PV=nRT). Temperature and internal energy have a direct relationship.

An ideal gas undergoes a cyclic process as shown on the graph above of pressure P versus volume V.

During which process is no work done on or by the gas?

• AB

• BC

• CD

• DE

• EA

Answer explanation

Work done is equivalent the area under the curve. Work done for process AB is zero since there is no area under the curve (and volume is constant).When volume is constant, no work is done.

An ideal gas undergoes a cyclic process as shown on the graph above of pressure P versus volume V.

At which point is the gas at its highest temperature?

• A

• B

• C

• D

• E

Answer explanation

At each point, you are given a triple of information. Pressure, volume and temperature. While temperature is not read off the graph, you can solve for temperature by using the ideal gas law (PV=nRT).

A certain quantity of an ideal gas initially at temperature T₀, pressure p₀, and volume V₀ is compressed to one-half its initial volume. As shown above, the process may be adiabatic (process 1), isothermal (process 2), or isobaric (process 3).

Which of the following is true of the mechanical work done on the gas?

• It is greatest for process 1.

• It is greatest for process 3.

• It is the same for processes 1 and 2 and less for process 3.

• It is the same for processes 2 and 3 and less for process 1.

• It is the same for all three processes.

Answer explanation

Work is equivalent to the area under the curve. The greater the area, the greater the work done.

A certain quantity of an ideal gas initially at temperature T₀, pressure p₀, and volume V₀ is compressed to one-half its initial volume. As shown above, the process may be adiabatic (process 1), isothermal (process 2), or isobaric (process 3).

Which of the following is true of the final temperature of this gas?

• It is greatest for process 1.

• It is greatest for process 2.

• It is greatest for process 3.

• It is the same for processes 1 and 2.

• It is the same for processes 1 and 3.

Answer explanation

Process 2 is isothermal. The temperature remains the same. Process 3 does have a change in temperature but at a lower pressure. Using the ideal gas law (PV=nRT), you can see the relationship between the three quantities.

A gas is taken from state i to state f along the two-step process shown in the PV diagram above.

How much work is done on the gas during the process described?

• 0 J

• 2,000 J

• 4,000 J

• 8,000 J

• 16,000 J

Answer explanation

Calculate area under the curve or use the work equation (W = P Vf-Vi)

A gas is taken from state i to state f along the two-step process shown in the PV diagram above.

What is the ratio Tf / Ti of the temperature of state f to the temperature of state i?

• 1

• 4/3

• 3/2

• 2

• 4

A monatomic ideal gas is initially in state A, as shown in the PV diagram above. The gas undergoes a transition from state A by the three different processes shown, where process III is isothermal.

Positive work is performed on the gas in which of the following processes?

• I only

• III only

• I and II only

• II and III only

• I, II, and III

A monatomic ideal gas is initially in state A, as shown in the PV diagram above. The gas undergoes a transition from state A by the three different processes shown, where process III is isothermal.

Energy is added to the gas by heating in which ofthe following processes?

• I only

• III only

• I and II only

• II and III only

• I, II, and III