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GASES
Chemistry 1-2
Mr. Chumbley
Modern Chemistry: Chapter
11
p. 340 – 377
MEASURING TEMPERATURE
AND PRESSURE
EQ: How are
temperature and
pressure
measured?
TEMPERATURE
There are many different ways in which temperature can be measured
 degrees Fahrenheit (˚F)
 degrees Celsius (˚C)
 Kelvin (K)
Converting between the different measurement systems can be done
using specific relationships
FAHRENHEIT AND CELSIUS
To convert from Fahrenheit to Celsius
℃ = ℉ − 32 × 5 9
To convert from Celsius to Fahrenheit
℉ = ℃ × 9 5 + 32
SAMPLE
What is the corresponding temperature, in degrees Celsius, of 65˚F?
What is the corresponding temperature, in degrees Fahrenheit, of
215˚C?
KELVIN
Kelvin is an absolute scale of temperature where a change of 1 K is
equal to 1 ˚C
To convert to Kelvin from Celsius
K = ℃ + 273
To convert to Celsius from Kelvin
℃ = K − 273
SAMPLE
The cosmic background temperature is a value for the average
temperature of space. It has a value of approximately 2.6 K
 What is this temperature in ˚C?
 What is this temperature in ˚F?
GASES AND PRESSURE
EQ: What is
pressure and
how is it
measured?
READING TASK
Read: Chapter 11, Section 1, pages 341 to 344
Take notes on key information (not just the highlighted
words)
There are three questions I have to help guide your notes:
 What causes gases to exert pressure?
 What is the tool used to measure atmospheric pressure,
and how does it work?
 What are the units in which pressure is commonly
measured?
PRESSURE
Pressure (P) is defined as the force per unit area on a surface
Pressure is caused by the collision of gas molecules
As gas particles collide with each other, and then on other objects they
exert a force on those objects
MEASURING PRESSURE
The device used to measure
atmospheric pressure is called a
barometer
Barometers originally used
mercury and a vertical column to
measure the pressure
A manometer is used to measure
the pressure of gases other than
the atmosphere
MEASURING PRESSURE
Like temperature there are multiple ways of measuring pressure
Millimeters of mercury (mm Hg) is the initial measure of atmospheric
pressure
One atmosphere of pressure (atm) is defined as being exactly
equivalent to 760 mm Hg
The pascal (Pa) is the SI unit of pressure
 One pascal is the pressure of one newton of force acting on an area of one square
meter
UNITS OF PRESSURE
Unit
Symbol
Conversion
atm
1 atm = 1 atm
Pa
1 atm = 1.013 x 105 Pa
1 atm = 101.3 kPa
mm Hg
1 atm = 760 mm Hg
torr
torr
1 atm = 760 torr
pounds per square inch
psi
1 atm = 14.7 psi
atmosphere
pascal
millimeter of mercury
SAMPLE PROBLEM 11A
The average atmospheric pressure in Denver, Colorado, is 0.830 atm.
Express this pressure in
 millimeters of mercury (mm Hg)
 kilopascals (kPa)
 pounds per square inch (psi)
THE GAS LAWS
EQ: What are the
mathematical
relationships between
pressure, volume, and
temperature?
BOYLE’S LAW
Boyle’s Law states that the
volume of a fixed mass of gas
varies inversely with the pressure
at constant temperature
𝑃1𝑉1 = 𝑃2𝑉2
SAMPLE 11C (P. 350)
A sample of oxygen gas has a volume of 150.0 mL when the
pressure is 0.947 atm. What will the volume of the gas be at a
pressure of 0.987 atm if the temperature remains constant?
Given:
P1 = 0.947 atm
V1 = 150 mL
P2 = 0.987 atm
Unknown:
V2 = ?
PRACTICE!
P. 371 – #18
P. 350 – Practice #1
GAS LAW AND SCUBA DIVING
Watch this video
Read the passage on p. 348 and answer the questions at the end of
the reading
Then, watch this video
THE GAS LAWS
EQ: What are the
mathematical
relationships between
pressure, volume, and
temperature?
CHARLES’S LAW
Charles’s Law states
that the volume of a
fixed mass of gas at
constant pressure varies
directly with the
temperature in Kelvin
𝑉1 𝑉 2
=
𝑇1 𝑇 2
SAMPLE 11D (P. 352)
A sample of neon gas occupies a volume of 752 mL at
25˚C. What volume will the gas occupy at 50˚C if the
pressure remains constant?
Given:
V1 = 752 mL
T1 = 298 K
T2 = 323 K
Unknown:
V2 = ?
PRACTICE!
P. 371 – #19
P. 352 – Practice D
GAY-LUSSAC’S LAW
Gay-Lussac’s law states
that the pressure of a
fixed mass of gas at
constant volume varies
directly with the
temperature in Kelvin
𝑃1 𝑃2
=
𝑇1 𝑇 2
SAMPLE 11E (P. 353)
The gas in a container is at a pressure of 3.00 atm at
25˚C. Directions on the container warn the user not to keep
it in a place where the temperature exceeds 52˚C. What
would be the gas pressure in the container at 52˚C?
Given:
P1 = 3.00 atm
T1 = 298 K
T2 = 325 K
Unknown:
P2 = ?
PRACTICE!
P. 372 – #19
P. 354 – Practice E
COMBINED GAS LAW
The combined gas law
expresses the
relationship between
pressure, volume, and
temperature of a fixed
amount of gas
𝑃1𝑉1 𝑃2𝑉2
=
𝑇1
𝑇2
SAMPLE 11F (P. 355)
A helium filled balloon has a volume of 50.0 L at 25˚C and 1.08 atm.
What volume will it have at 0.855 atm and 10˚C?
Given:
P1 = 1.08 atm
P2 = 0.855 atm
V1 = 50.0 L
T1 = 298 K
Unknown:
V2 = ?
T2 = 283 K
WHITEBOARDING!
For whiteboarding
today, make sure you
address the following in
your presentation:
 What variable, if any,
were held constant
 What gas law was
used
 Solution to the problem
Card Number
Problem
Number
2
#2
3
#3
5
#5
6
#6
8
#8
9
#9
Jack
#11
Queen
#12
CONVERSIONS AND EQUATIONS
Temperature Conversions
℃ = ℉ − 32 × 5 9
℉ = ℃ × 9 5 + 32
K = ℃ + 273
℃ = K − 273
Pressure Conversions
1 atm = 760 torr = 760 mm Hg = 101.3 kPa = 14.7 psi
Gas Laws
𝑃1𝑉1 = 𝑃2𝑉2
𝑉1 𝑉2
=
𝑇1 𝑇2
𝑃1 𝑃2
=
𝑇1 𝑇2
𝑃1𝑉1 𝑃2𝑉2
=
𝑇1
𝑇2
Ideal Gases
1 mol = 22.4 L
at STP
𝑃𝑉 = 𝑛𝑅𝑇
𝑅 = 0.0821
L ∙ atm
mol ∙ K
GAS VOLUMES AND THE IDEAL
GAS LAW
EQ: How can the
conditions of a
gas be fully
described?
REACTION OF GASES
Gases react in whole-number ratios according to
their volumes
For example, 2 volumes of hydrogen react with 1
volume of oxygen to yield 2 volumes of water
vapor
This means that when looking at reactions of
gases, the coefficients in a balanced chemical
equation reflect the ratio of volumes of reactants
and products
VOLUME OF GASES
When two gaseous substances are under the
same conditions, they contain equal numbers of
molecules
Avogadro’s law states that equal volumes of gases
at the same temperature and pressure contain
equal numbers of molecules
VOLUME OF GASES
All gases have the same volume under standard conditions
The standard molar volume of gas is the volume of one mole
of gas at standard temperature and pressure
This volume is 22.4 L/mol
Standard temperature and pressure (STP) is the conditions of
1 atm and 0˚C
SAMPLE PROBLEM 11G (P. 361)
a. What volume does 0.0685 mol of gas occupy at STP?
b. What quantity of gas, in moles, is contained in 2.21 L
at STP?
IDEAL GAS LAW
The physical characteristics of pressure, volume, and temperature are related
to the amount of gas
The ideal gas law is the mathematical relationship among pressure, volume,
temperature, and the number of moles of a gas
𝑃𝑉 = 𝑛𝑅𝑇
R is the ideal gas constant and it has a different value depending on the units
chosen
 The value we will use is when pressure is in atmospheres (atm), volume in liters
(L), and temperature in kelvin (K)
 This value is 0.0821
L∙atm
mol∙K
SAMPLE PROBLEM 11I (P. 365)
What is the pressure, in atmospheres, exerted by
a 0.500 mol sample of nitrogen gas in a 10.0 L
container at 298 K?