Free Study Guide for
Cracolice • Peters
Introductory Chemistry: An Active Learning Approach
Second Edition
www.brookscole.com/chemistry
Chapter 4
Introduction to Gases
Chapter 4–Assignment A: Physical Properties of Gases, Gas Measurements
We understand the structure and character of gases better than we understand the structure
and character of solids and liquids. Gases give us the clearest picture of the kinetic
molecular theory, on which we base our understanding of the differences between gases,
liquids, and solids. Kinetic molecular theory, which you may want to review, is introduced in
Chapter 2. Look for the following big ideas:
1)
The ideal gas model describes the activity of molecules in a sample of a gas. This
model has been derived to explain the measurable properties of a gas.
2)
The measurable properties of a gas are pressure, volume, temperature, and
quantity.
3)
In the laboratory, pressure is usually measured by a manometer. While finding
pressure from manometer readings is not included in the Chapter 4 Goals, the
procedure is given in the caption to Figure 4.7.
4)
Pressure may be expressed in the following units: atmospheres, centimeters or
millimeters of mercury, torr, pascals or kilopascals. In the USCS, pressure is
measured in inches of mercury or pounds per square inch.
5)
Equation 4.5 relates temperature measured in kelvins and degrees Celsius:
TK = T°C + 273.
Learning Procedures
Study
Sections 4.1–4.3. Focus on Goals 1–2 as you study.
Strategy
Construct an outline as you study the assignment. Goal 1, which asks you to
interpret the ideal gas model, is conceptual in nature. Try to construct a
“mental movie” of gases as you study the features of the ideal gas model.
Goal 2 relates a number of pressure units to one another. Check with your
instructor to see which units you are responsible for learning, and then
memorize those relationships.
Answer
Questions, Exercises, and Problems 1–15. Check your answers with those at
the end of the chapter.
23
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Study Guide for Introductory Chemistry: An Active Learning Approach
Workbook
If your instructor recommends the Active Learning Workbook, do
Questions, Exercises, and Problems 1–15.
Chapter 4–Assignment B: Gas Laws, Direct and Inverse Proportionalities
We noted in Assignment 4–A that the structure and character of gases are better understood
than the structure and character of liquids and solids. This has always been so. Most of the
early discoveries by the 18th and 19th century pioneers of experimental chemistry were
based on observations of gases. The high points of this assignment are:
1)
The Volume–Temperature (Charles') Law states that at constant pressure, the
volume of a fixed quantity of a gas is directly proportional to the absolute
temperature, V µ T.
2)
The Volume–Pressure (Boyle's) Law states that at constant temperature, the
volume of a fixed quantity of a gas is inversely proportional to its pressure,
V µ 1/P.
3)
For a fixed quantity of gas,
4)
Standard temperature
pressure, STP, are defined as 273 K and
† and †
1 atmosphere pressure.
P1V1
PV
= 2 2 . Given initial (or final) values of all three
T1
T2
variables and the final (or initial) values of two, the remaining value may be
calculated using the preceding equation.
Learning Procedures
Study
Sections 4.4–4.6. Focus on Goals 3–6 as you study.
Strategy
The emphasis in this assignment is on problem solving. The key to
succeeding in assignments like this is to practice, practice, practice by
solving all of the end-of-chapter problems and reflect on the errors you
make while doing the homework.
Answer
Questions, Exercises, and Problems 16–27. Check your answers with those
at the end of the chapter.
Workbook
If your instructor recommends the Active Learning Workbook, do
Questions, Exercises, and Problems 16–27.
Chapter 4–Assignment C: Summary and Review
A common mistake in solving pressure-volume-temperature questions is bad algebra. Be
careful in your thinking so you know which pressure or temperature you are coming from
and which pressure and temperature you are going to. Using a “tabular analysis” as shown
in the text helps to organize your thoughts. Some students label each quantity in the
question with a subscript 1 or 2 after reading the question. Find a way that works for you.
24
Copyright © 2004 Brooks/Cole, a division of Thomson Learning, Inc.
No part of this work may be reproduced without the written permission of the publisher.
Chapter 4
Introduction to Gases
You will understand these questions better if you reason your way through them. When
converting from a known volume to an unknown volume because of temperature and
pressure changes, a little proportional reasoning goes a long way. If the temperature goes
up, the volume must go up and vice versa. Look at the ratio of temperatures in your setup
and see if it is bigger than one, which will make the new volume bigger, or smaller than one,
which will make the new volume smaller. The same reasoning goes for the pressure ratio,
but in the opposite direction. If the pressure increases, the volume decreases, so the ratio of
pressures should be less than one and vice versa.
Also, remember to change all temperatures from °C to K.
Learning Procedures
Review
your lecture and textbook notes.
the Chapter in Review and the Key Terms and Concepts, and read the Study
Hints and Pitfalls to Avoid.
Answer
Concept-Linking Exercises 1–5. Check your answers with those at the end
of the chapter.
Questions, Exercises, and Problems 28–29. Include Questions 30–35 if
assigned by your instructor. Check your answers with those at the end of the
chapter.
Workbook
If your instructor recommends the Active Learning Workbook, do
Questions 28–32 if assigned by your instructor.
Take
the chapter summary test that follows. Check your answers with those at the
end of this assignment.
Chapter 4 Sample Test
1)
Pick the statement about the ideal gas model that is incorrect:
a) The volume of the particles, or molecules, is negligible compared to the volume
occupied by the gas.
b) There are large attractive forces between molecules in an ideal gas.
c) Intermolecular collisions occur without loss of kinetic energy.
d) Gas molecules are in constant motion.
e) Gas molecules are independent of each other.
2)
A pressure of 0.836 atmosphere is equal to:
a) 836 torr
b) 63.5 cm Hg
c) 732 mm Hg
d) 0.846 kPa
e) none of these
25
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No part of this work may be reproduced without the written permission of the publisher.
Study Guide for Introductory Chemistry: An Active Learning Approach
3)
A gas occupies 0.610 L at 0.103 atm pressure. What volume will the gas occupy at
1.62 atm pressure, if the temperature is held constant?
4)
A gas occupies 2.14 L at 40°C; what volume does this gas occupy if the temperature
is lowered to 20°C, with pressure remaining constant?
5)
Initially a gas occupies 4.80 L at 744 torr and 32°C. What volume will it fill at 811
torr and 64°C?
6)
A gas occupies 1.24 L at STP. Find the volume it will occupy at 21°C and 1.21
atmospheres.
26
Copyright © 2004 Brooks/Cole, a division of Thomson Learning, Inc.
No part of this work may be reproduced without the written permission of the publisher.
Chapter 4
Introduction to Gases
Answers to Chapter 4 Sample Test
1) b
3)
2) b
Initial Value (1)
Final Value (2)
V2 = V1 ¥
4)
6)
†
†
Temperature
40 + 273 = 313 K
20 + 273 = 293 K
Pressure
constant
constant
Temperature
32 + 273 = 305 K
64 + 273 = 337 K
Pressure
744 torr
811 torr
P1
T
744 torr
337 K
¥ 2 = 4.80 L ¥
¥
= 4.87 L
P2
T1
811 torr
305 K
Initial Value (1)
Final
(2)
† Value
†
V2 = V1 ¥
Pressure
0.103 atm
1.62 atm
T2
293 K
= 2.14 L ¥
= 2.00 L
T1
313 K
Volume
Initial Value (1) 4.80 L
Final
† Value (2) † V2
V2 = V1 ¥
Temperature
constant
constant
P1
0.103 atm
= 0.610 L ¥
= 0.0388 L
P2
1.62 atm
Volume
Initial Value (1) 2.14 L
Final
† Value (2) † V2
V2 = V1 ¥
5)
Volume
0.610 L
V2
Volume
1.24 L
V†2
Temperature
273 K
21†+ 273 = 294 K
Pressure
1 atm
1.21 atm
P1
T
1 atm
294 K
¥ 2 = 1.24 L ¥
¥
= 1.10 L
P2
T1
1.21 atm 273 K
†
†
27
Copyright © 2004 Brooks/Cole, a division of Thomson Learning, Inc.
No part of this work may be reproduced without the written permission of the publisher.