Download 10.2 PROCESSES 10.3 THE SECOND LAW OF

10.2 PROCESSES
10.3 THE SECOND LAW OF THERMO/ENTROPY
HW/Study Packet
HL
Required:
READ Hamper pp 86-94
Supplemental:
Tsokos, pp 174-192
REMEMBER TO….
Work through all of the ‘example problems’ in the texts as you are reading them
Refer to the IB Physics Guide for details on what you need to know about this topic
Refer to the Study Guides for suggested exercises to do each night
First try to do these problems using only what is provided to you from the IB Data Booklet
Refer to the solutions/key ONLY after you have attempted the problems to the best of your ability
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UNIT OUTLINE
I. THE FIRST LAW OF THERMODYNAMICS
A. SYSTEMS AND SURROUNDING
B. PV DIAGRAMS AND WORK DONE
II. TYPES OF PROCESSES
A. ISOCHORIC
B. ISOBARIC
C. ISOTHERMAL
D. ADAIBATIC
E. PV DIAGRAMS AND THERMODYNAMICS CYCLES
III. THE SECOND LAW OF THERMODYNAMICS
A. HEAT TRANSFER AND THE WAY THINGS NATURALLY HAPPEN
B. ENTROPY AND DISORDER
FROM THE IB DATA BOOKLET
WHAT YOU SHOULD BE ABLE TO DO AT THE END OF THIS TOPIC
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Understand the meaning of the term ‘internal energy’
Calculate the work done when a gas expands or contracts
State the relationship between changes in the internal energy, work done, and thermal energy
supplied through the first law of thermodynamics
Identify the first law of thermodynamics as a statement of the principle of energy conservation
Define the terms adiabatic, isothermal, isobaric, and isochoric and show these on a P-V diagram
Calculate the work done in a thermodynamic cycle from a P-V diagram
Understand what is meant by irreversibility and disorder and that entropy is a measure of
disorder
State the second law of thermodynamics in terms of entropy changes and heat transfer
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HOMEWORK PROBLEMS:
1. In a certain chemical process, a lab technician supplies 220 J of heat to a system, and at the same
time, 95 J of work are done on the system by its surroundings. What is the increase of internal
energy of the system?
[315 J]
2. A fixed mass of an ideal gas is heated at constant volume. If the
intenal energy at 1 was 450 J and the internal energy at 2 was 1200 J,
a) how much work has the system done?
[0 J]
b) what is the heat flow, and is it into or out of the system?
[+750 J]
P
2
1
V
c) The volume is held constant at 0.5 m3, the pressure at 1 is 2 x 105 Pa, and the temperature at 1
is T1 = 300 K. If the temperature at 2 is T2 450K what is the pressure at 2?
[300 kPa]
3. A gas in a piston expands from a volume of 0.060 m3 to a volume of 0.10 m3. The pressure in the
piston remains constant at a value of 4.0 x 105 Pa.
a) Is the gas gaining or losing energy? Why?
b) Is W positive or negative?
c) Calculate W.
[+16 kJ]
4. A piston moves so as to compress a gas. The gas stays at a constant pressure of 9 x 105 Pa. The
gas compresses by 100cm3.
a) Is W positive or negative for the gas? Why?
b) Calculate W.
[90 J]
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5. The diagram shows the pressure-volume (PV) diagram for one
cycle PQRS of an engine. In which sections of the cycle is work
done on the engine? Explain.
[PQ only]
6. The diagram shows the pressure p and volume V relationship
for one cycle of operation of an engine. Determine which parts
of the cycle identify isobaric, isochoric, and adiabatic changes
of state.
[isobaric I and III; isochoric IV; adiabatic II]
7. A thermodynamic system is taken from state a to c along
either path abc or path adc. Along path abc the work done W
by the system is 350 J. Along path adc W is 120 J. The
internal energies of the four states shown are Ua = 200 J, Ub =
280 J, Uc = 650 J and Ud = 360 J.
P
b
c
a
d
Calculate the heat flow Q for each of the four processes ab,
bc,ad, and dc. In each process, does the system absorb or
V
liberate heat?
[ab: +80 J, bc: +720 J, ad: +280 J, dc: +290 J]
8. An ideal gas undergoes the thermodynamic
changes represented in the P –V diagram (P
→ Q → R → P). What is the net work done by
the gas in a cycle?
[1.0 x 105 J]
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9. The P–V diagram shows the expansion of a fixed mass of an ideal gas, from state A to state
B. The temperature of the gas in state A is 400 K.
a) Calculate the temperature of the gas in state B. [400 K]
b) Calculate the work done by the gas in expanding from
state A to state B.
[2400 J]
c) Determine the amount of thermal energy transferred
during the expansion from state A to state B.
[2400 J]
The gas is isothermally compressed from state B back to state A.
d) Using the P–V diagram axes above, draw the variation of pressure with volume for this
isothermal compression.
e) State and explain whether the magnitude of the thermal energy transferred in this case
would be less than, equal to or greater than the thermal energy transferred in (c).
10. The cylinder shown below holds a volume V1 = 1000.0 cm3 of air at an initial pressure p1 = 1.10 x
105 Pa and temperature T1 = 300.0 K. Assume that air behaves like an ideal gas. The PV diagram
to the right shows a sequence of changes imposed on the air in the cylinder.
P2
C
piston
P1
P1
B
A
T1
V1
V2
a) From A B, the air is heated to 375 K at constant pressure. Calculate the new volume, V2.
[1250 cm3]
b) BC -the air is compressed isothermally to volume V1. Calculate the new pressure, P2.
[1.38 x 105 Pa
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11. A fixed mass of gas in a heat pump undergoes
a cycle of changes of pressure, volume and
temperature as illustrated in the graph to the
right. The gas is assumed to be ideal.
The table below shows the increase in internal
energy which takes place during each of the
changes A to B, B to C and C to D. It also
shows that in both of sections A to B and C to
D, no heat is supplied to the gas.
a) Using the first law of thermodynamics and necessary data from the graph, complete the table
below.
Increase in
Heat
Work done
Internal
supplied to
by gas (J)
Energy (J)
gas (J)
A to B
1200
0
B to C
-1350
C to D
-600
0
D to A
You will find it helpful to proceed in the following order, by finding the:
i) work done on gas for A to B and C to D
[AB: -1200 J, CD: +600 J]
ii) work done on gas for B to C and D to A
[BC: 0 J, DA: 0 J]
iii) heat supplied to gas for B to C
[-1350 J]
iv) increase in internal energy for D to A
[+750 J]
v) heat supplied to gas for D to A
[+750 J]
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