The Chemistry of
Gases
Unit 4
Chapter 12
12.1 Characteristics of
Gases
 Read Section 12.1 p. 416-422
Pre-assessment
Title: Crushed Bottle
This bottle was opened
at the top of Mount
San Jacinto. After it
was resealed, it was
then brought back
down to the bottom
of the mountain.
Discuss with a
neighbor and then
write a paragraph
explaining why it is
crushed.
12.1 Atmospheric
Pressure
 See p. 422
 Write a paragraph explaining what this
diagram is telling us.
Gases
Discuss and write down the names of three
chemicals which are gases.
Demo:
Marble + acid
Zinc + acid
Properties of gases:
 Gases are fluids
 Gases have low density
 Gases fill whatever container they are in
 Gases can be compressed
 Why? In a gas, the molecules are moving
around quickly and randomly
Notes
Pressure:
 caused by molecules
striking the wall of a
container
 Pressure = Force /
Area
 The SI unit of
pressure is the
Pascal (Pa)
 See Fig 6 p. 419
Barometer

Video clip: “Barometer – device to
calculate air pressure”
Writing assignment
Title: Barometer
See Fig 6 p. 419
Write a paragraph explaining how a
barometer works to measure air
pressure. Draw a diagram.
Some different units of
pressure p. 420
See Chem Ref Sheet: Define units
Pressure unit conversion
Convert a pressure of 225 kPa to
atmospheres.
ANSWER =
2.22 atm
Wanted: bring an empty soda can to class
Practice question
Convert a pressure of 2 atmospheres to
Pascals.
(hint: first convert atm to KPa, then convert
KPa to Pa)
ANS =
202 650 Pa
(Extras: Convert the local pressure to
Pascals)
Warm-up: pressure unit
conversion
1. Convert 426 mm mercury pressure to
Pascals
(Hint: first convert mm Hg to KPa (using conversion factor
on Chem Ref Sheet), then convert KPa to Pa)
ANS = 56795 Pa
2.Convert 12 444 Pascals pressure to mm
of mercury.
ANS = 93.338 mm Hg
Pressure unit conversion
Classwork p. 421 #1,2,3,4*
Be prepared for a quiz on pressure unit
conversions.
Suggested practice extras: p. 422 # 8,9,10
Worksheet
Kinetic Molecular Theory
CA Chemistry Standard
4b Students know the random motion of
molecules explains the diffusion of
gases.
Diffusion
Read p. 436 Diffusion
KWS:
Theprocesswhereparticlesmixastheresultoft
heirrandommovement
The process where particles mix as the
result of their random movement
Homogenous mixture: same throughout
Draw it!!
Sim: PhET gas properties
Standard Temperature and
Pressure (STP)
standardtemperatureandpressure(stp)isast
andardsetofconditionsforexperimentalme
asurementstoallowcomparisonstobemad
ebetweendifferentsetsofdata.
STPis1atmospherepressureand0°C
STP
Standard Temperature and Pressure (STP)
is a standard set of conditions for
experimental measurements, to allow
comparisons to be made between
different sets of data. STP is 1
atmosphere pressure and 0°C.
p. 420
CA Content Standard
4c. Students know how to apply the gas laws
to relations between the
 Pressure (P)
 Temperature (T)
 Volume (V)
of any amount of an ideal gas or any mixture
of ideal gases.
Combined Gas Law preview
Warm-up
In the following sentences, all the words
have been joined together and the
punctuation has been removed. Rewrite
the definition into correct English in your
notes:
‘in1662theenglishscientistrobertboylestudie
dtherelationshipbetweenthevolumeandth
epressureofagashefoundthatasthepressu
reonagasincreasesinaclosedcontainerthe
volumeofthegasdecreases’
Warm-up
‘In 1662, the English scientist Robert Boyle
studied the relationship between the
volume and the pressure of a gas. He
found that as the pressure on a gas
increases in a closed container, the
volume of the gas decreases.’
Think about it…..
 What happens to the pressure of a gas
when the volume is decreased?
(reminder: volume is the amount of space
something takes up)
The pressure increases.
Boyle’s Law
Pressure and volume are inversely
(directly/inversely) proportional
Boyle’s Law
Why?
Think Kinetic Molecular Theory
Sim: gas properties
Boyle’s Law
Boyle’s Law
P1= initial pressure
V1= initial volume
P2= final pressure
V2= final volume
Boyle’s Law
Practice question
A sample of gas occupies 523 mL at 1.00atm.
The volume of the gas is decreased to 265 mL,
while the temperature remains the same. What
is the new pressure of the gas?
GIVEN:
P1 = 1.00 atm
V1 = 523 mL
V2 = 265 mL
T1 = T2
UNKNOWN:
P2 = ? atm
Prediction: P2 < 1.00 atm OR P2 > 1.00 atm
Boyle’s Law Equation
Start with Combined Gas Law
When temperature is constant T1 = T2
P1V1 = P2V2
Boyle’s Law
Practice question
A sample of gas occupies 523 mL at 1.00atm.
The volume of the gas is decreased to 265 mL,
while the temperature remains the same. What
is the new pressure of the gas?
P1 = 1.00 atm
V1 = 523 mL
V2 = 265 mL
T1 = T2
UNKNOWN:
P2 = ? atm
Now, rearrange, substitute and solve…..
ANSWER =
1.97 atm
Boyle’s Law
Practice questions
Practice: p. 425 # 1-4
Then, complete Kinetic Molecular Theory
worksheet
Then, can you figure out Charles’s Law on
your own??? P. 428 #1-4
Learning Objective
Students know how to apply the gas laws to
relations between the
 Pressure (P)
 Temperature (T)
 Volume (V)
of any amount of an ideal gas or any mixture
of ideal gases.
Charles’s Law:
Think about it…..
 What happens to the volume of a balloon
if the temperature is increased?
Volume increases
Charles’s Law
T↑ V↑
T↓ V↓
(IF pressure is held constant)
V and T are directly proportional.
Charles’s Law
Charles’s Law
V1 V2

T1 T2
 Can be derived from Combined
Gas Law, if P1 = P2
 T must be converted to Kelvin.
Charles’s Law
(Can be derived from Combined Gas Law)
V1 V2

T1 T2
Rearrange eqn to solve for:
V2 = ?
T2 = ?
Chem Joke
Why shouldn’t you believe in atoms?
Because they make up everything 
Charles’s Law
Practice Problem
 A balloon is inflated to 665 mL volume at 27°C.
It is immersed in a dry-ice bath at −79°C. What
is its volume, assuming the pressure remains
constant?
First, need to convert the temperatures to Kelvin
T1 = 27oC = ?K
V1 = 665 mL
T2 = -79oC = ?K
V2 = ? mL
ANS =
430 mL
Charles’s Law Practice
Classwork
p.428 #1-4
Think about it……
 What happens to the pressure of a gas in
a balloon if the temperature is increased?
Think Kinetic Molecular theory
Gay-Lussac’s Law:
T↑ P↑
T↓ P↓
P is directly proportional to T
(IF volume is held constant)
Graphically…….
Mathematically…..
P1 P2

T1 T2
 Can be derived from
Combined Gas Law
 Temperature must be in
Kelvin
Practice question
A sealed can containing gas at 101 kPa and 22oC
is heated to 55oC. Calculate the pressure in
the heated can (assume volume is constant)
Use G.U.E.S.S.
Remember: convert oC to K
T1 = 22oC = ?K
P1 = 101 kPa
T2 = 55oC = ?K
ANSWER =
112 kPa
G-L Law Practice
p. 431 # 1-4 (Gay-Lussac's Law)
Early finishers: p. 432 #5-9
GAS
LAWS
Variables Constants
Boyle
Pressure
Volume
Temp
Charles
Temp
Volume
pressure
V1/T1=
V2/T2
Direct
GayLussac
Pressure
temp
Volume
P1/T1=
P2/T2
Direct
Equation
Proportionality
P1V1=P2V2 Inverse
Avagadro’s Law
in1811theitalianscientistAvagadroproposedt
heideathatequalvolumesofallgasesundert
hesameconditionshavethesamenumberof
particles
In 1811, the Italian scientist Avagadro
proposed the idea that equal volumes of
all gases under the same conditions,
have the same number of particles.
p.431
Avagadro’s Law
Fig. 15 p.431
See Chemistry Reference Sheet
What is STP?
What is an Ideal gas? Read p. 433
Puppies are cute
Avagadro’s Law Practice
 What is the volume of 3 moles of gas at
STP?
 G: moles
 U: volume
 Mol  volume conversion
 Conversion factor: 1 mol = 22.4L
ANSWER =
67.20 L
Practice
 How many moles of gas occupy a
volume of 112 L at STP?
 Volume  mol
ANSWER =
5 mol
Molar volume practice
 How many moles of gas occupy a volume of
73.2 L at STP?
 Same as, how many pairs of jeans could you
buy if you have $73.20 (one pair costs
$22.40)?
 G: volume (L)
 U: moles
 Volume  mol
 ANSWER =
 3.27 mol
Practice: Gas Laws
 A sample of neon gas starts out at STP.
What will be the pressure of the gas if the
Kelvin temperature is doubled (while the
volume is held constant)?
ANS =
2 x 1 atm = 2 atm
Review
What is the volume of
STP?
22.4L

What is the volume of
22.4 L

What is the volume of
STP?
22.4L

What is the volume of

1 mole of carbon dioxide at
1 mole of oxygen gas at STP?
1 mole of hydrogen gas at
1 mole of any gas at STP
Molar volume practice
2/19
A sample of gas at STP has a volume of
8.24 L. Calculate the number of moles of
gas in the sample.
Same as: How much pizza can you buy if
you have $8.24 and one pizza costs
$22.40
ANSWER =
0.368 mol
Gas stoichiometry
practice
 In an experiment, we burn 10 g of carbon.
What volume of carbon dioxide gas will be
formed if the gas is collected at STP?
p.441
Gas stoichiometry
practice
Step 1:
Given: 10 grams C
Unknown: ? moles C
 Conversion factor: Need atomic mass of C
Calculate moles of C
Gas stoichiometry
practice
Step 2:
Given: 0.83 mol C
Unknown: ? mol CO2
 Need balanced chemical equation for
combustion of carbon
 Conversion factor: Need molar ratio of C:CO2
Calculate moles of CO2
Gas stoichiometry
practice
In an experiment, we burn 10 g of carbon. What
volume of carbon dioxide gas will be formed if the
gas is collected at STP?
Step 3:
Given: 0.83 mol CO2
Unknown: ? L CO2
 Conversion factor: 1 mol = 22.4 L
 ANSWER = 19 L
Gas Stoichiometry
practice
 In the combustion reaction of 149 g of
propane (C3H8) with excess oxygen gas,
what volume of carbon dioxide is produced at
STP?
Step 1: mass propane  mol propane
need molar mass propane
Step 2: mol propane  mol CO2
need balanced chem equation
Step 3: mol CO2  volume CO2
use 22.4 L/mol
ANSWER =
227 L
Gas Stoichiometry extra
practice
 In the combustion reaction of 149 g of
butane (C4H10) with excess oxygen, what
volume of carbon dioxide is produced at
STP?
ANSWER =
230L
Think about it?
 A sealed can contains a gas at 101 kPa
and 300 K. It is heated to 600 K.
Calculate the new pressure of the gas in
the heated can (assume volume is
constant)
A) 50.5 kPa
B) 101 kPa
C) 202 kPa
D) 404 kPa
Soda Can mini-lab
Work in designated teams of 4; need safety glasses
 Pour ~40 mL of water into empty soda can
 Place soda can on hotplate and set hotplate to “12
o’clock position”
 Take your seat and wait until water is boiling vigorously
(you will see steam coming out the top)
~~~~~~~~~~~~~~~~~~~~~~~
 Using tongs:





carefully lift can from hotplate
quickly turn can upside down, and
Sink open end into water bath
What did you observe?
Soda Can mini-lab
Predict
Write a sentence predicting what will happen when the
soda can is inverted and submerged in the water bath.
Observe
Write a sentence describing your observation when the
soda can was inverted and submerged in the water bath.
Explain
Write a paragraph explaining the science of what
happened to the gas inside the can (think kinetic
molecular theory)
Oops!!
Learning Objective
* Students know how to solve problems by
using the ideal gas law in the form PV =
nRT.
Ideal Gas Law
PV = nRT
P = Pressure (atm or kPa)
V = Volume (L)
n = number of moles of gas
R = ‘Ideal Gas Constant’
(depends upon given pressure units)
T = temperature (K)
Ideal Gas Law
PV = nRT
Algebra practiceRearrange to solve for:
P=
V=
n=
T=
Practice: Ideal Gas Law
 p. 435 # 1-4 (P given in kPa)
 Green book p. 61 #1,7,9 (P given in atm)
Think about it….
Warm-up: 2/20
1. What pressure and temperature do STP
correspond to?
2. What is the volume of 1 mole of ideal gas at
STP?
3. Convert 430K to degrees Celsius
4. A sample of neon gas occupies a volume of
30 L at STP. What will be the temperature of
the gas if the pressure is doubled (while the
volume is held constant)?