UNIT 5 – GASES AND ATMOSPHERIC CHEMISTRY
Unit Expectations:
Page References
After completing this unit, the student should be able to:
1) State the properties of solids, liquids and gases.
Note, 418-422
2) Use the Particle Theory of Matter to explain the properties of solids, liquids
and gases.
Note, 418-419
3) State and define the three types of molecular motion.
Note, 418-419
4) State the five assumptions of the Kinetic Molecular Theory of Gases and
use them to explain the properties of gases.
421
5) Name the device used to measure atmospheric pressure and explain
how it works.
426
6) Carry out conversions involving pressure, temperature or volume units.
Note, 428, 440
7) a) State Boyle's Law in words and mathematically.
b) Draw graphs to represent Boyle's Law.
c) Use Boyle's Law to solve problems.
Note, 432-434
8) a) State Charles' Law in words and mathematically.
b) Draw a graph to represent Charles' Law.
c) Use Charles' Law to solve problems.
Note, 440-446
9) a) State Gay-Lussac's Law in words and mathematically.
b) Draw a graph to represent Gay-Lussac's Law.
c) Use Gay-Lussac's Law to solve problems.
Note, 447-449
10) Solve problems involving the combined gas law.
Note, 452-457
11) a) State Dalton's Law of Partial Pressures.
b) Use Dalton's Law of Partial Pressures to solve problems.
Note, 459-460
12) Solve gas law problems involving gases collected over water.
Note, 507-509
13) State Avogadro's Hypothesis and solve problems related to it.
Note, 473-481
14) Describe and explain the behaviour of real gases.
482-483
15) Use the ideal gas law to solve problems.
Note, 484-493
16) Calculate the molar mass of a gas from experimental data.
Note, 494-495
17) a) State Gay-Lussac’s Law of Combining Volumes and solve problems
related to it.
b) Carry out other stoichiometric calculations involving gases.
Note, 501-511
1
THE KINETIC MOLECULAR THEORY AND STATES OF MATTER
The Particle Theory of Matter:
1) All matter is made up of tiny particles.
2) All particles of one substance are the same. Different substances are made of different
particles.
3) There are spaces between the particles.
4) There are attractive forces between the particles.
5) The particles are always moving.
The Properties of the States of Matter:
Property
Solids
Liquids
Gases
Attractive Forces
Between Particles
Amount of Space
Between Particles
Motion
of Molecules
Volume
Shape
Degree of
Compressibility
Changes of State: All changes of state are caused by breaking of or forming of bonds
between particles.
Melting – change of state from solid to liquid.
Freezing – change of state from liquid to solid.
Evaporation (or Vapourization) – change of state from liquid to gas.
Condensation (or Liquefaction) – change of state from gas to liquid.
Sublimation – change of state from solid to gas or gas to solid.
States of Matter
2
THREE TYPES OF MOTION
VIBRATIONAL MOTION
ROTATIONAL MOTION
TRANSLATIONAL MOTION
Solids, Liquids and Gases
3
THE KINETIC MOLECULAR THEORY
Gases are ______________ from the other states of matter. The BIGGEST differences are
the ______________ between the particles, and the _____________ of those particles with
each other.
Gases are the only substance whose volumes are ___________________, and therefore
related to the _______________________________of the surroundings.
Gases will expand when heated and can be squeezed into small containers. Their shape
will always be determined by the shape of their container.
The ___________________________________ attempts to explain the behaviour of gases
by examining gas particles at the _________________ level. It is based around the first
postulate of the _____________________________, which states: “All substances are
composed of a large number of very small particles called atoms or molecules.”
The Kinetic Molecular Theory of Gases begins with ____________________ that describe
the behaviour of molecules in a gas. These postulates are based upon some simple, basic
scientific notions, but they also involve some simplifying assumptions. In reading a postulate,
do two things. First, try to understand and appreciate the basic physical idea embodied in the
postulate; this idea will ultimately be important in understanding the macroscopic properties
of the gas in terms of the behaviour of the microscopic molecules making up the gas.
Second, identify possible weakness or flaws in the postulates. Inaccurate predictions by a
theory derive from flawed postulates used in the derivation of the theory.
Postulates
1.
2.
3.
4.
5.
Because of these 5 postulates, we are able to call the gases that we study __________
gases. Gases do not behave ______________ in the real world, but we will pretend that
they do.
Kinetic Molecular Theory
4
EXERCISE – THE STATES OF MATTER
Read pages 414 to 419 in your text.
Then, using the information on those pages and today’s class note, answer the following
questions:
1) Name the change of state involved when:
a) dew forms on grass on a cool summer night.
b) moth balls placed in a drawer of clothing disappear.
c) hot liquid butter cools and hardens.
d) ice crystals form on the sides of a freezer.
e) ice in a glass of pop disappears.
f) frost forms on a car windshield.
g) dry ice disappears in a warm room.
2) Use the Particle Theory of Matter to explain each of the following:
a) Solids melt when heated.
b) Changes of state are physical changes.
c) Gases diffuse (spread out) rapidly.
d) Your skin feels cool when a liquid evaporates from it.
e) The densities of gases are much lower than those of liquids and solids.
f) Gases are more compressible than liquids.
Also, do Questions 4 to 7 on page 423.
EXERCISE – KINETIC MOLECULAR THEORY AND IDEAL VS REAL GASES
Read pages 421-422
1) State the five assumptions associated with the kinetic molecular theory of gases. (Just the
first sentence from each assumption is enough.)
2) Why is it useful to have a theory of an ideal gas based on the kinetic molecular theory of
gases?
Also, do Qu. 2, 3 (pg. 435); Qu. 4 (pg. 451).
Then, read pg. 482-483 and do Qu. 4 (pg. 521).
5
BOYLE’S LAW AND UNITS OF MEASUREMENT
Unit Conversions
1) Pressure
Pressure is an exerted force that is the result of the collision of gas molecules with the
surface of a container. The more frequent the collisions, the higher the pressure.
There are four units of pressure, kilopascals (kPa), millimeters of mercury (mmHg),
atmospheres (atm) and Torr (torr).
101.3 kPa = 760 mmHg = 1.00 atm = 760 torr
Example Convert 710 mmHg into kPa
2) Volume
Volume is usually measured in litres (L) or milliliters (mL).
1 L = 1000 mL
3) Temperature
Temperature is the measure of the kinetic energy of the particles in a sample of molecules.
The higher the temperature, the more energy the particles possess.
Temperature is measured in Celsius (oC) or Kelvin (K).
The Kelvin temperature scale is based on the theoretical point where all molecular
movement would stop. This point is known as absolute zero, 0 Kelvin or -273oC.
oC
273 K
6
Standard Temperature and Pressure (STP) and Standard Ambient
Temperature and Pressure (SATP)
Scientists use STP and SATP in their experiments. If a question says that the gas is at
STP, that means the
Temperature =
Pressure =
If a question says that the gas is at SATP, that means the
Temperature =
Pressure =
BOYLE’S LAW PROBLEMS
Boyle’s Law
The volume of a gas is inversely proportional to its pressure, as long as the
temperature is constant.
Mathematically,
V1P1 = V2P2
Example
100 L of a gas is at a pressure of 22 kPa. If the pressure increases to 44 kPa, what is the
volume?
Notice that the units cancel. If they do not, then you must do unit conversions so that they will
cancel.
7
EXERCISE - CONVERSIONS AND BOYLE’S LAW PROBLEMS
Do Section Review Qu. 1, 4, 5 (pg. 435); Pract. Problems 1 to 3 (pg. 434-435); 5, 6 (pg. 446).
(You can check your answers to these questions on page 469.)
Also, do the following questions:
1)
Do the following conversions:
a) 0.250 L to mL
b) 85 cm3 to L
2) A tire with a volume of 500 cm3 is at standard pressure. What would the volume become if
the pressure was increased to 150 kPa?
3) The initial pressure on a gas is 150 kPa. What is the final pressure if the gas is compressed
to half of its original volume?
4) If a quantity of gas measures 400 mL at 1.50 atm., calculate its volume at 600 kPa.
5) Calculate the pressure of the gas in the globe when the piston shown in the diagram below
is pushed in to the end of the syringe body.
6) Calculate the pressure of the gas in the globes shown below when the valve connecting
the two globes is opened.
Answers
1) a) 250 mL
b) 0.085 L
2) 338 cm3
3) 300 kPa
4) 101 mL
5) 79 kPa
6) 22 kPa
8
THE GAS LAWS
Boyle’s Law:
Charles’ Law:
Gay-Lussac’s Law:
Put all these laws together and we get The Combined Gas Law
Example:
10.0 L of a gas is at STP. What would be the volume at 25ºC?
Example:
1.010 L of a gas is at 106 kPa and -3 ºC. What would the temperature be if the pressure is
changed to 0.864 atm and the volume becomes 820 mL?
9
EXERCISE - GAS LAW PROBLEMS
Do Practice Problems 8 to 11 (pg. 446); 13 to 15 (pg. 449-450); 17 to 21 (pg. 457).
(You can check your answers to these questions on page 469.)
Also, do the following questions:
1) In passing through a turbine electrical generator, 1.0 L of steam at 300C and 3500 kPa
pressure expands to 55 L and has its temperature lowered to 110C. What is the pressure of
the steam leaving the turbine?
2) The temperature and pressure of the gas mixture produced in the main engines of the space
shuttle are 2000C and 5.0 x 108 kPa. Calculate the volume to which each cubic metre (1.0
m3) of this gas mixture expands when it has been ejected into the upper atmosphere where
the pressure is 10 kPa and the temperature is 30C.
3) A store has a helium gas cylinder which is used to fill balloons. The helium gas cylinder has
a volume of 1.5 L, a pressure of 1.50 x 104 kPa and is in a room kept at 23C. The balloons
being filled each have a volume of 2.55 L and maintain a temperature and pressure at 15C
and 115 kPa respectively. Calculate how many balloons the tank is capable of filling.
Answers
1)
42 kPa
2) 5.3 x 106 m3
3) 74 balloons can be filled. ( Some gas is left over in the cylinder.)
10
MORE GAS LAWS
Dalton’s Law of Partial Pressures
The total pressure of a mixture of gases is the sum of the pressures of each of the individual
gases. (pg 459)
PTOTAL = P1 + P2 + P3 + ….
Avogadro’s Hypothesis
Equal volumes of all ideal gases at the same temperature and pressure contain the same
number of molecules. (pg 473)
The number of moles of a gas is directly proportional to the volume if the temperature and
pressure remain constant.
V1n2 = V2n1
The spaces between gas molecules are HUGE compared to the size of the molecules
themselves. Since space (volume) is determined by temperature and pressure, the same
volumes of gas at the same temperature have essentially the same number of particles (moles).
Molar Volume
This is the volume of one mole of gas. It is measured in L/mol. At STP all ideal gases have a
molar volume of 22.4L/mol. (pg 474)
VSTP = n(22.4L/mol)
The Ideal Gas Law
Boyle’s Law, Charles Law, Gay-Lussac’s Law and Avogardro’s Hyphothesis were combined to
derive the Ideal Gas Law. (pg 484)
PV = nRT
P = pressure (kPa)
V = volume (L)
n = moles (mol)
T = temperature (K)
R = 8.314 kPa.L/mol.K
11
Examples
1) Calculate the molar volume of a gas at 20oC and 2.000 atm.
2) 1.42L of a gas at STP has a mass of 4.74g. Calculate its molar mass.
3) Calculate the density of carbon dioxide gas at 25oC and 110kPa.
12
EXERCISE – DALTON’S LAW OF PARTIAL PRESSURES
Do Practice Problems 22, 23, 25 (pg. 460).
( You can check your answers to these questions on page 469.)
Also, do the following questions:
1) The total pressure of a mixture of hydrogen, helium and argon is 99.3 kPa. If the partial
pressure of helium is 42.7 kPa and the partial pressure of argon is 54.7 kPa, what is the
partial pressure of hydrogen?
2) A gas mixture consists of 60.0% argon, 30.0% neon and 10.0% krypton. If the pressure of
this gas mixture is 80.0 kPa, what is the partial pressure of each of the gases?
3) Air is a mixture of many gases. The partial pressure of nitrogen is 80.0 kPa. The partial
pressure of oxygen is 20.3 kPa. If the atmospheric pressure is 101.3 kPa, what is the
combined partial pressure of all the other gases present in air?
Answers
1)
1.9 kPa
2)
48.0 kPa Ar, 24.0 kPa Ne, 8.00 kPa Kr
3)
1.0 kPa
___________________________________________________________________________
THE IDEAL GAS LAW AND AVOGADRO’S HYPOTHESIS
Do Practice. Problems 5,7 (pg. 482); 12, 14, (pg. 487-488); 20, 21 (pg. 500).
Also, do Section Review Questions 1, 3, 4, 5 (pg. 488).
( You can check your answers to these questions on page 523 except for #14 which
should
be 23.2 L.)
Also, do the following questions:
1)
Calculate the density of acetylene (C2H2) in grams per litre at STP.
2) How many grams of carbon dioxide are contained in a sample that occupies 1.09 L at
127C and 40.5 kPa?
3) Calculate the molar mass of a compound that has a density of 1.87 g/L at STP.
4) a) How many moles of oxygen molecules are there in 50.0 L of oxygen gas at STP?
b) How many individual oxygen molecules are there in the 50.0 L of gas?
5) Calculate the volume that 1.00 x 1024 helium gas atoms occupy at STP.
6) An evacuated flask is found to have a mass of 110.020g. When filled with O 2, the flask
has a mass of 110.660g. When filled with an unknown gas (X), it has a mass of 110.380g.
a) Calculate the molar mass of gas X. (Hint: See Avogadro’s Hypothesis – pg. 473.)
b) Is the unknown gas He, H2, F2 or H2O?
Answers
1) 1.16 g/L
2) 0.584g
3) 41.9 g/mol
4) a) 2.23 mol
5) 37.2 L
6)
a)
b)
18.0 g/mol
13
1.34 x 1024 molecules
b)
H2O
COLLECTION AND ANALYSIS OF GASES BY
DISPLACEMENT OF WATER
(see pg 507 for water vapour pressures)
Water displacement is a convenient
method of collecting gases that have
low water solubility.
The water is displaced by the gas
due to density. The gas is less
dense than the water. It rises to the
top of the tube and forces the water
out.
The only issue with this type of gas
collection is that the pressure
contributed by the water vapour
(gaseous water) must be taken into consideration when calculating the pressure of the collected
gas. (Remember Dalton’s Law of Partial Pressures?)
Example
a) 0.0460 g of unknown gas occupies 360 mL when collected over water at 20˚C and an
atmospheric pressure of 80.00 kPa. Calculate the molar mass of the gas.
b) Which of the following is most likely to be the chemical formula of the gas?
He
H2
F2
CO2
14
MOLECULAR FORMULA OF A GAS
Example
A gas is made up of 80.0% C and 20.0% H. 4.60 g of this gas occupies a volume of 2.50 L
at 1.50 atm and 25.0˚C. Calculate the molecular formula of the gas .
15
EXERCISE – COLLECTION AND MOLECULAR FORMULA OF A GAS
1) If oxygen is collected over water at 18C and an atmospheric pressure of 101.30 kPa, what
is the pressure of the oxygen?
2) A student collects nitrogen over water at an atmospheric pressure of 100.70 kPa and 21C.
What is the pressure of the nitrogen?
3) 0.2907g of an unknown gas occupies 280 mL when collected over water at 25C and an
atmospheric pressure of 95.00 kPa.
a) Calculate the molar mass of the gas.
b) Which of the following is most likely to be the chemical formula of the gas:
Cl2, SO2, O2, N2 ?
4) A compound was found to contain 54.5% C, 9.1% H and 36.4% O. The vapour from 0.082g
of the compound occupied 21.6 mL at 20C and 104.0 kPa. Calculate the molecular
formula of this compound.
Also, do Practice Problem 24 and Section Review Question 3 on page 500.
(You can check your answers to these questions on page 523.)
Answers
1)
99.24 kPa 2)
98.21 kPa 3)
a)
28.0 g/mol b)
N2
4)
C4H8O2
___________________________________________________________________________
EXERCISE: APPLICATIONS OF GASES
1) Read page 437.
a) Explain how cryogenic freezing is useful with respect to transplants.
b) What are superconductors and what can they be used for?
2) Read pages 450-451.
a) What are the two most common safety devices that are installed in compressed gas
cylinders?
b) When is it not suitable to install these safety devices in a compressed gas cylinder?
3) Read page 426 and do Qu. 11 (pg. 467). Also, answer the following question:
For each of the following locations or situations, would you cook an egg less than or more
than five minutes to produce a “five minute” boiled egg that is cooked to the same extent as
it would be at SATP. Explain your answers.
a) You are making breakfast during a skiing trip at the top of Whistler Mountain in British
Columbia.
b) You have breakfast just before you start work 2000 m underground in a gold mine in
Timmins, Ontario.
c) You have breakfast on a very clear and bright sunny day.
d) You have breakfast on a very gloomy, rainy day.
Also, read pages 458, 462-464 and do Qu. 7, 9 page 467.
16
GAS LAW STOICHIOMETRY
1. Volume – Volume
Calculate the volume of CO2 (g) which will be produced from 8.40 L of O2 (g) at STP
during the combustion of CH3OH (l).
2. Mass-Volume Problem
Calculate the volume of CO2 (g) which will be produced from 75.3 g of O2 (g) during the
combustion of CH3OH(l) at 30ºC and 738 mmHg.
17
3. Collection of Gases Over Water – Stoichiometry
A student reacts 1.09 g of calcium with excess hydrobromic acid to produce hydrogen
gas.
(a) What volume of dry hydrogen would be collected over water at 28ºC and 101.80 kPa?
(b) If the student actually obtained 625 mL of hydrogen gas, calculate the % yield.
4. Gas Law Stoich – Limiting Reagent
How many litres of CO2 (g) will be produced at 25ºC and 150 kPa when 8.77 L of CH4(g)
react with 15.9 g of O2(g)?
18
EXERCISE – GAS LAW STOICHIOMETRY – COLLECTION OVER
WATER AND LIMITING REACTANT PROBLEMS
Do Questions 28, 29, (pg. 522); Practice. Problem 30 (pg. 506).
( You can check your answers to these questions on pages 646, 523 except for #28 which
should be 3.10 L.)
Also, do the following questions:
1) How many litres of H2 (at STP) will form when 6.71g of Al react with 12.95g of H2SO4?
2Al(s) + 3H2SO4(aq)  Al2(SO4)3(aq) + 3H2(g)
5) What volume of SO2 will be produced at 35C and 110 kPa when 20.9g of FeS react with
10.0 L of O2 in a closed container?
4FeS(s) + 7O2(g)  2Fe2O3(s) + 4SO2(g)
6) What volume of ammonia gas can be synthesized if 15 L of nitrogen is reacted with 25 L of
hydrogen? (All measurements are at STP.)
7) What mass of iron(III) oxide can be produced when 255g of iron(II) sulphide is reacted
with 50.0 L of oxygen in a closed container to produce iron(III) oxide and sulphur dioxide
gas? (All measurements are at STP.)
Answers
1)
2.96 L
2)
5.53 L
3)
17 L
4)
102g
___________________________________________________________________________
ATMOSPHERIC REACTIONS AND POLLUTION
Do Question 8 page 467. ( See page 459 to find the answer.)
Read pages 515-519. Then, do questions 2, 3, 4 (pg. 520) and question 9 (pg. 521).
19
UNIT 5 – REVIEW QUESTIONS
(Please note that the purpose of this sheet is to give you some practice questions to help you
prepare for the test. It does not have every type of question on it. The complete list of what
you are responsible for knowing for the Unit 5 test is on the Unit 5 Expectations sheet.)
1) The lung capacity of a scuba diver at the surface of the water is 3200 mL at 17C and
standard pressure. The diver goes to a depth where the pressure is 202 kPa and the
temperature is 7C. Calculate the volume of air that his lungs could hold at that depth.
2) A balloon holds 1.0L of a gas at 25C and 1.0 atm of pressure. The gas is then heated to
45C. What pressure must be applied to force the volume to remain constant?
3) 3 gases are placed in a container. The partial pressures of the component gases are:
N2 0.35 atm, O2 0.23 atm, Cl2 0.56 atm
What is the total pressure of the mixture?
4) A rigid metal tank is filled with CO2 gas. The pressure is recorded at 12 atm and the
temperature is 27C. If the tank is heated to 87C, what pressure is now exerted by the gas
in the tank?
5) At 25C the volume of a gas sample is 380 mL. To what temperature must the gas sample
be heated so its final volume becomes 760 mL?
6) A gas occupies 25.0 L at 92C and 0.960 atm. At what temperature will the gas occupy a
volume of 40.0 L at a pressure of 0.990 atm?
7) Calculate the volume of 2.20g of carbon dioxide gas at STP.
8) 500 cm3 of a gas at STP has a mass of 2.0g. Calculate the molar mass of the gas.
9) Calculate each of the following:
a) the volume of 2.00 mol of chlorine at STP.
b) the volume of 4.00 mol of nitrogen at STP.
10) How many moles are there in each of the following:
a) 896 mL of chlorine gas at STP?
b) 4.48 L of nitrogen gas measured at 273°C and 50 kPa?
11) 0.646g of an unknown gas occupies 1.00 L when collected over water at 27°C and
95.00 kPa atmospheric pressure. Calculate the molar mass of the gas.
12) Calculate the density of carbon dioxide gas at STP.
Answers:
1)
2)
3)
4)
1.55 x 103 mL
1.1 atm
1.14 atm
14 atm
5)
6)
7)
8)
323C
329C
1.12 L
90 g/mol
9) a) 44.8 L b) 89.6 L
10) a) 0.0400 mol b) 0.049 mol
11) 17.6 g/mol
12) 1.96 g/L
20
UNIT 5 – REVIEW QUESTIONS (PART 2)
(Please note that the purpose of this sheet is to give you some practice questions to help you
prepare for the test. It does not have every type of question on it. The complete list of what
you are responsible for knowing for the Unit 5 test is on the Unit 5 Expectations sheet.)
1) A compound contains 46.1% C and 53.9% N. 2.1 g of this gaseous compound occupy
992 mL at 21°C and 99.3 Kpa. Calculate the simplest formula and the molecular formula
of this compound.
2) Molten sodium chloride decomposes when an electrical current is passed through it. How
many millilitres of chlorine gas will be produced at 500C and 101.3 kPa from 1.00g of
sodium chloride?
3) If 3.5 kg of Fe is produced by the following reaction, what volume, at STP, of CO 2
would be produced? Fe2O3(s) + 3CO(g)  2Fe(s) + 3CO2(g)
4) How many grams of carbon dioxide will be produced when 8.50 g of methane (CH 4)
undergo combustion with 22.26 L of oxygen gas at STP?
Answers:
1)
2)
3)
4)
CN, C2N2
542 mL
2.1 x 103 L
21.9g
21