introductory chemistry , 2 nd edition nivaldo tro
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Introductory Chemistry , 2 nd Edition Nivaldo Tro. Chapter 11 Gases. Roy Kennedy Massachusetts Bay Community College Wellesley Hills, MA. 2006, Prentice Hall. Gases Pushing. gas molecules are constantly in motion as they move and strike a surface, they push on that surface push = force - PowerPoint PPT PresentationTRANSCRIPT
Roy KennedyMassachusetts Bay Community College
Wellesley Hills, MA
Introductory Chemistry, 2nd EditionNivaldo Tro
Chapter 11Gases
2006, Prentice Hall
Tro's Introductory Chemistry, Chapter
2
Gases Pushing• gas molecules are constantly in motion• as they move and strike a surface, they
push on that surfacepush = force
• if we could measure the total amount of force exerted by gas molecules hitting the entire surface at any one instant, we would know the pressure the gas is exertingpressure = force per unit area
Tro's Introductory Chemistry, Chapter
3
The Effect of Gas Pressure• the pressure exerted by a gas can cause
some amazing and startling effects• whenever there is a pressure
difference, a gas will flow from area of high pressure to low pressure the bigger the difference in pressure, the
stronger the flow of the gas
• if there is something in the gas’ path, the gas will try to push it along as the gas flows
Tro's Introductory Chemistry, Chapter
4
Soda Straws & Gas Pressure
The pressure of theair inside the straw isthe same as the pressureof the air outsidethe straw – so liquid levels isthe same on bothsides.
The pressure of theair inside the straw is
lower than the pressureof the air outside
the straw – so liquid is pushedup the straw bythe outside air.
Tro's Introductory Chemistry, Chapter
5
Air Pressure• the atmosphere exerts a pressure
on everything it contactson average 14.7 psi the atmosphere goes up about 370
miles, but 80% is in the first 10 miles from the earth’s surface
• this is the same pressure that a column of water would exert if it were about 10.3 m high
Tro's Introductory Chemistry, Chapter
6
Properties of Gases
• expand to completely fill their container
• take the shape of their container
• low densitymuch less than solid or liquid state
• compressible
• mixtures of gases are always homogeneous
• fluid
Tro's Introductory Chemistry, Chapter
7
Kinetic Molecular Theory
• the particles of the gas, (either atoms or molecules), are constantly moving
• the attraction between particles is negligible• when the moving particles hit another
particle or the container, they do not stick; but they bounce off and continue moving in another directionlike billiard balls
Tro's Introductory Chemistry, Chapter
8
Kinetic Molecular Theory
• there is a lot of empty space between the particlescompared to the size of the particles
• the average kinetic energy of the particles is directly proportional to the Kelvin temperatureas you raise the temperature of the gas, the average
speed of the particles increasesbut don’t be fooled into thinking all the particles are
moving at the same speed!!
Tro's Introductory Chemistry, Chapter
9
Kinetic Molecular Theory
Tro's Introductory Chemistry, Chapter
10
Gas Properties Explained
• Gases have indefinite shape and volume because the freedom of the molecules allows them to move and fill the container they’re in
• Gases are compressible and have low density because of the large spaces between the molecules
Tro's Introductory Chemistry, Chapter
11
Properties – Indefinite Shape and Indefinite Volume
Because the gasmolecules have enough kineticenergy to overcomeattractions, theykeep moving aroundand spreading outuntil they fill the container
As a result, gasestake the shape andthe volume of thecontainer they are in.
Tro's Introductory Chemistry, Chapter
12
Properties - Compressibility
Because there is a lot of unoccupied space in the structureof a gas, the gas molecules can be squeezed closer together
Tro's Introductory Chemistry, Chapter
13
Properties – Low Density
Because there is a lot of unoccupied space in the structureof a gas, gases have low density
Tro's Introductory Chemistry, Chapter
14
The Pressure of a Gas• result of the constant
movement of the gas molecules and their collisions with the surfaces around them
• the pressure of a gas depends on several factorsnumber of gas particles in a
given volumevolume of the containeraverage speed of the gas
particles
Tro's Introductory Chemistry, Chapter
15
Measuring Air Pressure• use a barometer• column of mercury
supported by air pressure
• force of the air on the surface of the mercury balanced by the pull of gravity on the column of mercury
gravity
Tro's Introductory Chemistry, Chapter
16
Atmospheric Pressure & Altitude• the higher up in the atmosphere you go,
the lower the atmospheric pressure is around youat the surface the atmospheric pressure is
14.7 psi, but at 10,000 ft is is only 10.0 psi
• rapid changes in atmospheric pressure may cause your ears to “pop” due to an imbalance in pressure on either side of your ear drum
Tro's Introductory Chemistry, Chapter
17
Pressure Imbalance in Ear
If there is a differencein pressure acrossthe eardrum membrane,the membrane will bepushed out – what we commonly call a “popped eardrum.”
Tro's Introductory Chemistry, Chapter
18
Common Units of PressureUnit Average Air Pressure at
Sea Level
pascal (Pa) 101,325
kilopascal (kPa) 101.325
atmosphere (atm) 1 (exactly)
millimeters of mercury (mmHg) 760 (exactly)
inches of mercury (inHg) 29.92
torr (torr) 760 (exactly)
pounds per square inch (psi, lbs./in2) 14.7
Example 11.1:Converting Between
Pressure Units
Tro's Introductory Chemistry, Chapter
20
Example:• A high-performance road bicycle is inflated to a total
pressure of 125 psi. What is the pressure in millimeters of mercury?
Tro's Introductory Chemistry, Chapter
21
Example:A high-performance road bicycle is inflated to a total pressure of 125 psi. What is the pressure in millimeters of mercury?
• Write down the given quantity and its units.
Given: 125 psi
Tro's Introductory Chemistry, Chapter
22
• Write down the quantity to find and/or its units.
Find: ? mmHg
Information
Given: 125 psi
Example:A high-performance road bicycle is inflated to a total pressure of 125 psi. What is the pressure in millimeters of mercury?
Tro's Introductory Chemistry, Chapter
23
• Collect Needed Conversion Factors:
14.7 psi = 760 mmHg
Information
Given: 125 psi
Find: ? mmHg
Example:A high-performance road bicycle is inflated to a total pressure of 125 psi. What is the pressure in millimeters of mercury?
Tro's Introductory Chemistry, Chapter
24
• Write a Solution Map for converting the units :
Information
Given: 125 psi
Find: ? mmHg
CF: 14.7 psi = 760 mmHg
psi mmHg
psi 14.7
mmHg 607
Example:A high-performance road bicycle is inflated to a total pressure of 125 psi. What is the pressure in millimeters of mercury?
Tro's Introductory Chemistry, Chapter
25
• Apply the Solution Map:
mmHg psi 14.7
mmHg 760psi 251
= 6.46259 x 103 mmHg = 6.46 x 103 mmHg • Sig. Figs. & Round:
InformationGiven: 125 psiFind: ? mmHgCF: 14.7 psi = 760 mmHgSM: psi → mmHg
Example:A high-performance road bicycle is inflated to a total pressure of 125 psi. What is the pressure in millimeters of mercury?
the 760 is an exact numberand does not effect thesignificant figures
Tro's Introductory Chemistry, Chapter
26
• Check the Solution:
125 psi = 6.46 x 103 mmHg
The units of the answer, mmHg, are correct.The magnitude of the answer makes sense
since mmHg are smaller than psi.
InformationGiven: 125 psiFind: ? mmHgCF: 14.7 psi = 760 mmHgSM: psi → mmHg
Example:A high-performance road bicycle is inflated to a total pressure of 125 psi. What is the pressure in millimeters of mercury?
Tro's Introductory Chemistry, Chapter
27
Boyle’s Law• pressure of a gas is inversely
proportional to its volumeconstant T and amount of gasgraph P vs V is curvegraph P vs 1/V is straight line
• as P increases, V decreases by the same factor
• P x V = constant
• P1 x V1 = P2 x V2
Tro's Introductory Chemistry, Chapter
28
Boyle’s Experiment• added Hg to a J-tube with
air trapped inside• used length of air column
as a measure of volume
Length of Airin Column
(in)
Difference inHg Levels
(in)48 0.044 2.840 6.236 10.132 15.128 21.224 29.722 35.0
Tro's Introductory Chemistry, Chapter
29
Boyle's Expt.
0
20
40
60
80
100
120
140
0 10 20 30 40 50 60
Volume of Air, in3
Pre
ssu
re, in
Hg
Tro's Introductory Chemistry, Chapter
30
Inverse Volume vs Pressure of Air, Boyle's Expt.
0
20
40
60
80
100
120
140
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09
Inv. Volume, in-3
Pre
ss
ure
, in
Hg
Tro's Introductory Chemistry, Chapter
31
Boyle’s Experiment, P x VPressure Volume P x V
29.13 48 140033.50 42 140041.63 34 140050.31 28 140061.31 23 140074.13 19 140087.88 16 1400
115.56 12 1400
Tro's Introductory Chemistry, Chapter
32
When you double the pressure on a gas,the volume is cut in half, (as long as the
temperature and amount of gas do not change)
Tro's Introductory Chemistry, Chapter
33
Boyle’s Law & Breathing• inhale
diaphragm & rib muscles contractchest cavity expands - volume increasepressure inside lungs drops below air pressureair flows into lung to equilibrate pressure
gases move from hi pressure to low
• exhalediaphragm & rib muscles relaxchest cavity volume decreasespressure inside lungs rises above air pressureair flows out of lung to equilibrate pressure
• normal healthy person can generate a lung pressure of 1.06 atm
Tro's Introductory Chemistry, Chapter
34
Boyle’s Law and Diving• since water is denser than
air, for each 10 m you dive below the surface the pressure on your lungs increases 1 atmat 20 m the total pressure
is 3 atm
• if your tank contained air at 1 atm pressure you would not be able to inhale it into your lungs
Tro's Introductory Chemistry, Chapter
35
Boyle’s Law and Diving• scuba tanks have a regulator
so that the air in the tank is delivered at the same pressure as the water surrounding you
• if a diver holds her breath and rises quickly, so that the outside pressure drops to 1 atm; according to Boyle’s Law, what should happen to the volume of air in the lungs?
Tro's Introductory Chemistry, Chapter
36
Which Way Would Air Flow?
Tro's Introductory Chemistry, Chapter
37
Is this possible at a depth of 20 m?
Example 11.2:Boyle’s Law
Tro's Introductory Chemistry, Chapter
39
Example:• A cylinder equipped with a
moveable piston has an applied pressure of 4.0 atm and a volume of 6.0 L. What is the volume if the applied pressure is decreased to 1.0 atm?
Tro's Introductory Chemistry, Chapter
40
Example:A cylinder equipped with a moveable piston has an applied pressure of 4.0 atm and a volume of 6.0 L. What is the volume if the applied pressure is decreased to 1.0 atm?
• Write down the given quantity and its units.
Given: P1 = 4.0 atm V1 = 6.0 L
P2 = 1.0 atm
Tro's Introductory Chemistry, Chapter
41
• Write down the quantity to find and/or its units.
Find: V2, L
Information
Given: P1 = 4.0 atm V1 = 6.0 L
P2 = 1.0 atm
Example:A cylinder equipped with a moveable piston has an applied pressure of 4.0 atm and a volume of 6.0 L. What is the volume if the applied pressure is decreased to 1.0 atm?
Tro's Introductory Chemistry, Chapter
42
• Collect Needed Equation:
The relationship between pressure and volume is Boyle’s Law
Information
Given: P1 = 4.0 atm V1 = 6.0 L
P2 = 1.0 atm
Find: V2 = ? L
Example:A cylinder equipped with a moveable piston has an applied pressure of 4.0 atm and a volume of 6.0 L. What is the volume if the applied pressure is decreased to 1.0 atm?
2211 VPVP
Tro's Introductory Chemistry, Chapter
43
• Write a Solution Map:
P1, V1, P2 V2
Information
Given: P1 = 4.0 atm V1 = 6.0 L
P2 = 1.0 atm
Find: V2 = ? L
Eq’n: P1 ∙ V1 = P2 ∙ V2
Example:A cylinder equipped with a moveable piston has an applied pressure of 4.0 atm and a volume of 6.0 L. What is the volume if the applied pressure is decreased to 1.0 atm?
2211 VPVP
when using this equation, the units of P1 and P2 must be the same,or you will have to convert one to the other
for the same reason, the units of V2 must be L to match the unit of V1
Tro's Introductory Chemistry, Chapter
44
• Apply the Solution Map:
• Sig. Figs. & Round:
Information
Given: P1 = 4.0 atm V1 = 6.0 L
P2 = 1.0 atm
Find: V2 = ? L
Eq’n: P1 ∙ V1 = P2 ∙ V2
SM: P1, V1, P2 → V2
Example:A cylinder equipped with a moveable piston has an applied pressure of 4.0 atm and a volume of 6.0 L. What is the volume if the applied pressure is decreased to 1.0 atm?
L 24V
atm 1.0
L 6.0atm 4.0
VP
VP
VPVP
2
22
11
2211
Tro's Introductory Chemistry, Chapter
45
• Check the Solution:
V2 = 24 L
The units of the answer, L, are correct.The magnitude of the answer makes sense -
since the pressure is decreasing the volume should be increasing.
Information
Given: P1 = 4.0 atm V1 = 6.0 L
P2 = 1.0 atm
Find: V2 = ? L
Eq’n: P1 ∙ V1 = P2 ∙ V2
SM: P1, V1, P2 → V2
Example:A cylinder equipped with a moveable piston has an applied pressure of 4.0 atm and a volume of 6.0 L. What is the volume if the applied pressure is decreased to 1.0 atm?
Temperature Scales
Celsius Kelvin Fahrenheit-273°C-269°C
-183°C
-38.9°C
0°C
100°C
0 K4 K
90 K
234.1 K
273 K
373 K
-459 °F-452°F
-297°F
-38°F
32°F
212°F
Absolute Zero
BP Helium
BP Oxygen
BP Mercury
MP Ice
BP Water
0 R7 R
162 R
421 R
459 R
671 R
Rankine
Tro's Introductory Chemistry, Chapter
47
Standard Conditions
• Common reference points for comparing
• standard pressure = 1.00 atm
• standard temperature = 0°C273 K
• STP
Tro's Introductory Chemistry, Chapter
48
Volume and Temperature• In a rigid container, raising the temperature
increases the pressure• For a cylinder with a piston, the pressure
outside and inside stay the same• To keep the pressure from rising, the piston
moves out increasing the volume of the cylinderas volume increases, pressure decreases
Tro's Introductory Chemistry, Chapter
49
Volume and Temperature
As a gas is heated, it expands.This causes the density of thegas to decrease. Because the hot air in theballoon is less dense than thesurrounding air, it rises.
Tro's Introductory Chemistry, Chapter
50
Charles’ Law• volume is directly proportional to
temperatureconstant P and amount of gasgraph of V vs T is straight line
• as T increases, V also increases• Kelvin T = Celsius T + 273• V = constant x T
if T measured in Kelvin
2
2
1
1
T
V
T
V
51
Charle's Law & Absolute Zero
0
0.1
0.2
0.3
0.4
0.5
0.6
-300 -250 -200 -150 -100 -50 0 50 100 150
Temperature, °C
Vo
lum
e, L
Volume (L) of 1 g O2 @ 1500 torr
Volume (L) of 1 g O2 @ 2500 torr
Volume (L) of 0.5 g O2 @ 1500 torr
Volume (L) of 0.5 g SO2 @ 1500 torr
We’re losing altitude.Quick Professor, give yourlecture on Charles’ Law!
Tro's Introductory Chemistry, Chapter
53
Absolute Zero
• theoretical temperature at which a gas would have zero volume and no pressureKelvin calculated by extrapolation
• 0 K = -273.15 °C = -459 °F = 0 R• never attainable
though we’ve gotten real close!
• all gas law problems use the Kelvin temperature scale!
Tro's Introductory Chemistry, Chapter
54
Determining Absolute Zero
William Thomson,the Lord of Kelvin,extrapolated theline graphs ofVolume vs. Temp.to determine thetheoretical temp.a gas would havea volume of 0.
Example 11.3:Charles’ Law
Tro's Introductory Chemistry, Chapter
56
Example:• A sample of gas has a
volume of 2.80 L at an unknown temperature. When the sample is submerged in ice water at 0°C, its volume decreases to 2.57 L. What was the initial temperature in kelvin and in celsius? (assume constant pressure)
Tro's Introductory Chemistry, Chapter
57
Example:A gas has a volume of 2.80 L at an unknown temperature. When the sample is at 0°C, its volume decreases to 2.57 L. What was the initial temperature in kelvin and in celsius?
• Write down the given quantity and its units.
Given: V1 = 2.80 L
V2 = 2.57 L t2 = 0°C
Tro's Introductory Chemistry, Chapter
58
• Write down the quantity to find and/or its units.
Find: temp1, in K and °C
Information
Given: V1 = 2.80 L
V2 = 2.57 L t2 = 0°C
Example:A gas has a volume of 2.80 L at an unknown temperature. When the sample is at 0°C, its volume decreases to 2.57 L. What was the initial temperature in kelvin and in celsius?
Tro's Introductory Chemistry, Chapter
59
• Collect Needed Equation:
The relationship between temperature and volume is Charles’ Law
Information
Given: V1 = 2.80 L
V2 = 2.57 L t2 = 0°C
Find: temp1 in K and °C
Example:A gas has a volume of 2.80 L at an unknown temperature. When the sample is at 0°C, its volume decreases to 2.57 L. What was the initial temperature in kelvin and in celsius?
2
2
1
1
T
V
T
V
Tro's Introductory Chemistry, Chapter
60
• Write a Solution Map:
V1, V2, T2 T1
when using this equation, the units of V1 and V2 must be the same,or you will have to convert one to the other
the units of T1 and T2 must be kelvin, K
Information
Given: V1 = 2.80 L
V2 = 2.57 L t2 = 0°C
Find: temp1 in K and °C
Eq’n:
Example:A gas has a volume of 2.80 L at an unknown temperature. When the sample is at 0°C, its volume decreases to 2.57 L. What was the initial temperature in kelvin and in celsius?
2
2
1
1
T
V
T
V
2
2
1
1
T
V
T
V
Tro's Introductory Chemistry, Chapter
61
• Apply the Solution Map:
Information
Given: V1 = 2.80 L
V2 = 2.57 L t2 = 0°C
Find: temp1 in K and °C
Eq’n:
SM: V1, V2 T2 → T1
Example:A gas has a volume of 2.80 L at an unknown temperature. When the sample is at 0°C, its volume decreases to 2.57 L. What was the initial temperature in kelvin and in celsius?
2
2
1
1
T
V
T
V
1
112
21
2
2
1
1
T K 297
TL 2.57
K 273L 802 T
V
TV
T
V
T
V
.
K 273 T
273 0 T
273 C)(t(K)T
2
2
22
Tro's Introductory Chemistry, Chapter
62
• Apply the Solution Map:convert to celsius
Information
Given: V1 = 2.80 L T1 = 297 K
V2 = 2.57 L t2 = 0°C, T2 = 273 K
Find: temp1 in K and °C
Eq’n:
SM: V1, V2 T2 → T1
Example:A gas has a volume of 2.80 L at an unknown temperature. When the sample is at 0°C, its volume decreases to 2.57 L. What was the initial temperature in kelvin and in celsius?
2
2
1
1
T
V
T
V
C 24 t
273 297 t
273 (K)TC)(t
1
1
11
Tro's Introductory Chemistry, Chapter
63
• Check the Solution:
T1 = 297 K or t1 = 24 °C
The units of the answer, K and °C, are correct.The magnitude of the answer makes sense -
since the volume is decreasing the temperature should be decreasing.
Information
Given: V1 = 2.80 L T1 = 297 K
V2 = 2.57 L t2 = 0°C, T2 = 273 K
Find: temp1 in K and °C
Eq’n:
SM: V1, V2 T2 → T1
Example:A gas has a volume of 2.80 L at an unknown temperature. When the sample is at 0°C, its volume decreases to 2.57 L. What was the initial temperature in kelvin and in celsius?
2
2
1
1
T
V
T
V
Tro's Introductory Chemistry, Chapter
64
The Combined Gas Law• Boyle’s Law shows the relationship
between pressure and volumeat constant temperature
• Charles’ Law shows the relationship between volume and absolute temperatureat constant pressure
• the two laws can be combined together to give a law that predicts what happens to the volume of a sample of gas when both the pressure and temperature change
2
22
1
11
T
VP
T
VP
Example 11.4:The Combined Gas Law
Tro's Introductory Chemistry, Chapter
66
Example:• A sample of gas has an initial volume of 158 mL at a
pressure of 735 mmHg and a temperature of 34°C. If the gas is compressed to a volume of 108 mL and heated to 85°C, what is the final pressure in mmHg?
Tro's Introductory Chemistry, Chapter
67
Example:A sample of gas has a volume of 158 mL at a pressure of 735 mmHg and a temperature of 34°C. The gas is compressed to a volume of 108 mL and heated to 85°C, what is the final pressure in mmHg?
• Write down the given quantity and its units.
Given: V1 = 158 mL, P1 = 735 mmHg, t1 = 34°C
V2 = 108 mL, t2 = 85°C
Tro's Introductory Chemistry, Chapter
68
• Write down the quantity to find and/or its units.
Find: P2, mmHg
Information
Given: V1 = 158 mL, P1 = 755 mmHg,
t1 = 34°C
V2 = 108 mL, t2 = 85°C
Example:A sample of gas has a volume of 158 mL at a pressure of 735 mmHg and a temperature of 34°C. The gas is compressed to a volume of 108 mL and heated to 85°C, what is the final pressure in mmHg?
Tro's Introductory Chemistry, Chapter
69
• Collect Needed Equation:
The relationship between pressure, temperature and volume is the Combined Gas Law
2
22
1
11
T
VP
T
VP
Information
Given: V1 = 158 mL, P1 = 755 mmHg,
t1 = 34°C
V2 = 108 mL, t2 = 85°C
Find: P2, mmHg
Example:A sample of gas has a volume of 158 mL at a pressure of 735 mmHg and a temperature of 34°C. The gas is compressed to a volume of 108 mL and heated to 85°C, what is the final pressure in mmHg?
Tro's Introductory Chemistry, Chapter
70
• Write a Solution Map:
P1,V1, V2, T1, T2 P2
when using this equation, the units of V1 and V2, and the units of P1 and P2, must be the same, or you will have to convert one to the other
the units of T1 and T2 must be kelvin, K
2
22
1
11
T
VP
T
VP
2
22
1
11
T
VP
T
VP
Information
Given: V1 = 158 mL, P1 = 755 mmHg,
t1 = 34°C
V2 = 108 mL, t2 = 85°C
Find: P2, mmHg
Eq’n:
Example:A sample of gas has a volume of 158 mL at a pressure of 735 mmHg and a temperature of 34°C. The gas is compressed to a volume of 108 mL and heated to 85°C, what is the final pressure in mmHg?
Tro's Introductory Chemistry, Chapter
71
Information
Given: V1 = 158 mL, P1 = 755 mmHg,
t1 = 34°C
V2 = 108 mL, t2 = 85°C
Find: P2, mmHg
Eq’n:
SM: P1, V1, V2, T1, T2 → P2
• Apply the Solution Map:
23
2
221
211
2
22
1
11
P mmHg 10251
PmL 108K 307
K 358mL 158mmHg 557
PVT
TVP
T
VP
T
VP
.K 358 T
273 85 T
273 C)(t(K)T
2
2
22
K 307 T
273 34 T
273 C)(t(K)T
1
1
11
2
22
1
11
T
VP
T
VP
Example:A sample of gas has a volume of 158 mL at a pressure of 735 mmHg and a temperature of 34°C. The gas is compressed to a volume of 108 mL and heated to 85°C, what is the final pressure in mmHg?
Tro's Introductory Chemistry, Chapter
72
• Check the Solution:
P2 = 1.25 x 103 mmHg
The units of the answer, mmHg, are correct.The magnitude of the answer makes sense -
since the volume is decreasing and temperature is increasing the pressure should be increasing.
Information
Given: V1 = 158 mL, P1 = 755 mmHg,
t1 = 34°C → T1 = 307 K
V2 = 108 mL, t2 = 85°C → T2 = 358 K
Find: P2, mmHg
Eq’n:
SM: P1, V1, V2, T1, T2 → P2
2
22
1
11
T
VP
T
VP
Example:A sample of gas has a volume of 158 mL at a pressure of 735 mmHg and a temperature of 34°C. The gas is compressed to a volume of 108 mL and heated to 85°C, what is the final pressure in mmHg?
Tro's Introductory Chemistry, Chapter
73
Avogadro’s Law• volume directly proportional to
the number of gas moleculesV = constant x nconstant P and Tmore gas molecules = larger
volume
• count number of gas molecules by moles
• equal volumes of gases contain equal numbers of moleculesthe gas doesn’t matter
2
2
1
1
n
V
n
V
Tro's Introductory Chemistry, Chapter
74
Avogadro’s Law
Example 11.5:Avogadro’s Law
Tro's Introductory Chemistry, Chapter
76
Example:• A 4.8 L sample of helium gas contains 0.22 mol helium.
How many additional moles of helium must be added to obtain a volume of 6.4 L? (assume constant pressure and temperature)
Tro's Introductory Chemistry, Chapter
77
Example:A 4.8 L sample of helium gas contains 0.22 mol helium. How many additional moles of helium must be added to obtain a volume of 6.4 L?
• Write down the given quantity and its units.
Given: V1 = 4.8 L n1 = 0.22 mol
V2 = 6.4 L
Tro's Introductory Chemistry, Chapter
78
• Write down the quantity to find and/or its units.
Find: n2, mol; and moles added
Information
Given: V1 = 4.8 L, n1 =0.22
mol
V2 = 6.4 L
Example:A 4.8 L sample of helium gas contains 0.22 mol helium. How many additional moles of helium must be added to obtain a volume of 6.4 L?
Tro's Introductory Chemistry, Chapter
79
• Collect Needed Equation:
The relationship between temperature and volume is Avogadro’s Law
2
2
1
1
n
V
n
V
Information
Given: V1 = 4.8 L, n1 =0.22
mol
V2 = 6.4 L
Find: n2, mol and added mol
Example:A 4.8 L sample of helium gas contains 0.22 mol helium. How many additional moles of helium must be added to obtain a volume of 6.4 L?
Tro's Introductory Chemistry, Chapter
80
• Write a Solution Map:
V1, V2, n1 n2
when using this equation, the units of V1 and V2 must be the same,or you will have to convert one to the other
the units of n1 and n2 must be moles
2
2
1
1
n
V
n
V
2
2
1
1
n
V
n
V
Information
Given: V1 = 4.8 L, n1 =0.22
mol
V2 = 6.4 L
Find: n2, mol and added mol
Eq’n:
Example:A 4.8 L sample of helium gas contains 0.22 mol helium. How many additional moles of helium must be added to obtain a volume of 6.4 L?
Tro's Introductory Chemistry, Chapter
81
Information
Given: V1 = 4.8 L, n1 =0.22 mol
V2 = 6.4 L
Find: n2, mol and added molEq’n:
SM: V1, V2, n1 → n2
• Apply the Solution Map:
mol 290n
L 4.8
mol 0.22L .46n
V
n Vn
n
V
n
V
2
21
122
2
2
1
1
.
2
2
1
1
n
V
n
V
Example:A 4.8 L sample of helium gas contains 0.22 mol helium. How many additional moles of helium must be added to obtain a volume of 6.4 L?
Tro's Introductory Chemistry, Chapter
82
• Apply the Solution Map: to get the added moles, subtract n1 from n2
moles 0.07 moles added
0.22 0.29 moles added
n nmoles added 12
Information
Given: V1 = 4.8 L, n1 =0.22 mol
V2 = 6.4 L
Find: n2, mol and added molEq’n:
SM: V1, V2, n1 → n2
2
2
1
1
n
V
n
V
Example:A 4.8 L sample of helium gas contains 0.22 mol helium. How many additional moles of helium must be added to obtain a volume of 6.4 L?
Tro's Introductory Chemistry, Chapter
83
• Check the Solution:
n2 = 0.29 moles; added 0.07 moles
The units of the answer, moles, are correct.The magnitude of the answer makes sense -
since the volume is increasing the total number of moles should be increasing.
Information
Given: V1 = 4.8 L, n1 =0.22 mol
V2 = 6.4 L
Find: n2, mol and added molEq’n:
SM: V1, V2, n1 → n2
2
2
1
1
n
V
n
V
Example:A 4.8 L sample of helium gas contains 0.22 mol helium. How many additional moles of helium must be added to obtain a volume of 6.4 L?
Tro's Introductory Chemistry, Chapter
84
Ideal Gas Law• By combing the gas laws we can write a general
equation• R is called the Gas Constant• the value of R depends on the units of P and V
we will use 0.0821 and convert P to atm and V to L
• use the Ideal Gas law when have a gas at one condition, use the Combined Gas Law when you have gas whose condition is changing
Kmol
Latm
nRTPVor R
Tn
VP
Example 11.7:The Ideal Gas Law
Requiring Unit Conversion
Tro's Introductory Chemistry, Chapter
86
Example:• Calculate the number of moles of gas in a basketball
inflated to a total pressure of 24.2 psi with a volume of 3.2 L at 25°C
Tro's Introductory Chemistry, Chapter
87
Example:Calculate the number of moles of gas in a basketball inflated to a total pressure of 24.2 psi with a volume of 3.2 L at 25°C
• Write down the given quantity and its units.
Given: V = 3.2 L, P = 24.2 psi, t = 25°C
Tro's Introductory Chemistry, Chapter
88
• Write down the quantity to find and/or its units.
Find: n, mol
Example:Calculate the number of moles of gas in a basketball inflated to a total pressure of 24.2 psi with a volume of 3.2 L at 25°C
InformationGiven: V = 3.2 L, P = 24.2 psi,
t = 25°C
Tro's Introductory Chemistry, Chapter
89
• Collect Needed Equation:
The relationship between pressure, temperature, number of moles and volume is the Ideal Gas Law
InformationGiven: V = 3.2 L, P = 24.2 psi,
t = 25°CFind: n, mol
Example:Calculate the number of moles of gas in a basketball inflated to a total pressure of 24.2 psi with a volume of 3.2 L at 25°C
nRTPVor R
Tn
VP
Tro's Introductory Chemistry, Chapter
90
• Write a Solution Map:
P,V,T,R n
when using the Ideal Gas Equation, the units of V must be L; and the units of P must be atm, or you will have to convert
the units of T must be kelvin, K
InformationGiven: V = 3.2 L, P = 24.2 psi,
t = 25°CFind: n, molEq’n: PV = nRT
Example:Calculate the number of moles of gas in a basketball inflated to a total pressure of 24.2 psi with a volume of 3.2 L at 25°C
PV = nRT
Tro's Introductory Chemistry, Chapter
91
• Apply the Solution Map:convert the units
K 298 T
273 25 T
273 C)t(T(K)
InformationGiven: V = 3.2 L, P = 24.2 psi,
t = 25°CFind: n, molEq’n: PV = nRTSM: P,V,T,R → n
Example:Calculate the number of moles of gas in a basketball inflated to a total pressure of 24.2 psi with a volume of 3.2 L at 25°C
atm 62461psi 14.7
atm 1psi 24.2 P .
Tro's Introductory Chemistry, Chapter
92
• Apply the Solution Map:
InformationGiven: V = 3.2 L, P = 1.6462
atm, T = 298 K
Find: n, molEq’n: PV = nRTSM: P,V,T,R → n
Example:Calculate the number of moles of gas in a basketball inflated to a total pressure of 24.2 psi with a volume of 3.2 L at 25°C
mol 0.22 n
K 298 0.0821
L 23atm 62461n
TR
VP
TRnVP
Kmol
atmL
..
Tro's Introductory Chemistry, Chapter
93
• Check the Solution:
n = 0.22 moles
The units of the answer, moles, are correct.It is hard to judge the magnitude with so many variables,but with a volume less than 22.4 L at pressures near 1 atm
and temperatures near 273 K – it is reasonable tohave less than 1 mole of gas
InformationGiven: V = 3.2 L, P = 1.6462
atm, T = 298 K
Find: n, molEq’n: PV = nRTSM: P,V,T,R → n
Example:Calculate the number of moles of gas in a basketball inflated to a total pressure of 24.2 psi with a volume of 3.2 L at 25°C
Tro's Introductory Chemistry, Chapter
94
Molar Mass of a Gas
• one of the methods chemists use to determine the molar mass of an unknown substance is to heat a weighed sample until it becomes a gas, measure the temperature, pressure and volume, and use the Ideal Gas Law
moles
gramsin massMassMolar
Example 11.8:Molar Mass Using
The Ideal Gas Law anda Mass Measurement
Tro's Introductory Chemistry, Chapter
96
Example:• A sample of a gas has a mass of 0.311 g. Its volume
is 0.225 L at a temperature of 55°C and a pressure of 886 mmHg. Find its molar mass.
Tro's Introductory Chemistry, Chapter
97
Example:A sample of a gas has a mass of 0.311 g. Its volume is 0.225 L at a temperature of 55°C and a pressure of 886 mmHg. Find its molar mass.
• Write down the given quantity and its units.
Given: V = 0.225 L, P = 886 mmHg, t = 55°C
m = 0.311 g
Tro's Introductory Chemistry, Chapter
98
• Write down the quantity to find and/or its units.
Find: molar mass (g/mol)
InformationGiven: V = 0.225 L, P = 886
mmHg, t = 55°C, m = 0.311 g
Example:A sample of a gas has a mass of 0.311 g. Its volume is 0.225 L at a temperature of 55°C and a pressure of 886 mmHg. Find its molar mass.
Tro's Introductory Chemistry, Chapter
99
• Collect Needed Equations:
The relationship between pressure, temperature, number of moles and volume is the Ideal Gas Law
The relationship between mass and moles is the molar mass
InformationGiven: V = 0.225 L, P = 886
mmHg, t = 55°C, m = 0.311 g
Find: molar mass, (g/mol)
nRTPV
Example:A sample of a gas has a mass of 0.311 g. Its volume is 0.225 L at a temperature of 55°C and a pressure of 886 mmHg. Find its molar mass.
moles
gramsin massMassMolar
Tro's Introductory Chemistry, Chapter
100
• Write a Solution Map:
P,V,T,R n
when using the Ideal Gas Equation, the units of V must be L; and the units of P must be atm, or you will have to convert
the units of T must be kelvin, K
InformationGiven: V = 0.225 L, P = 886 mmHg,
t = 55°C, m = 0.311 gFind: molar mass, (g/mol)Eq’n: PV = nRT; MM = mass/moles
Example:A sample of a gas has a mass of 0.311 g. Its volume is 0.225 L at a temperature of 55°C and a pressure of 886 mmHg. Find its molar mass.
Molar Mass
mass
PV = nRT
Tro's Introductory Chemistry, Chapter
101
• Apply the Solution Map:convert the units
K 328 T
273 55 T
273 C)t(T(K)
mmHg 58611mmHg 760
atm 1mmHg 868 P .
InformationGiven: V = 0.225 L, P = 886 mmHg,
t = 55°C, m = 0.311 gFind: molar mass, (g/mol)Eq’n: PV = nRT; MM = mass/moles
SM: P,V,T,R → n & mass → mol. mass
Example:A sample of a gas has a mass of 0.311 g. Its volume is 0.225 L at a temperature of 55°C and a pressure of 886 mmHg. Find its molar mass.
Tro's Introductory Chemistry, Chapter
102
• Apply the Solution Map:
mol 100649.7 n
K 328 0.0821
L .2250atm 58611n
TR
VP
TRnVP
3-
Kmol
atmL
.
InformationGiven: V = 0.225 L, P = 1.1658 atm,
t = 328 K, m = 0.311 gFind: molar mass, (g/mol)Eq’n: PV = nRT; MM = mass/moles
SM: P,V,T,R → n & mass → mol. mass
Example:A sample of a gas has a mass of 0.311 g. Its volume is 0.225 L at a temperature of 55°C and a pressure of 886 mmHg. Find its molar mass.
g/mol 31.9 MassMolar
moles 109.7406
0.311gMassMolar
moles
gramsin massMassMolar
3-
Tro's Introductory Chemistry, Chapter
103
• Check the Solution:
molar mass = 31.9 g/mol
The units of the answer, g/mol, are correct.It is hard to judge the magnitude with so many variables.
InformationGiven: V = 0.225 L, P = 1.1658 atm,
t = 328 K, m = 0.311 gFind: molar mass, (g/mol)Eq’n: PV = nRT; MM = mass/moles
SM: P,V,T,R → n & mass → mol. mass
Example:A sample of a gas has a mass of 0.311 g. Its volume is 0.225 L at a temperature of 55°C and a pressure of 886 mmHg. Find its molar mass.
Tro's Introductory Chemistry, Chapter
104
Ideal vs. Real Gases
• Real gases often do not behave like ideal gases at high pressure or low temperature
• Ideal gas laws assume1) no attractions between gas molecules2) gas molecules do not take up space based on the Kinetic-Molecular Theory
• at low temperatures and high pressures these assumptions are not valid
Tro's Introductory Chemistry, Chapter
105
Ideal vs. Real
106
Mixtures of Gases• According to Kinetic Molecular Theory, the particles in
a gas behave independently• Air is a mixture, yet we can treat it as a single gas• Also, we can think of each gas in the mixture
independent of the other gases though all gases in the mixture have the same volume and
temperatureall gases completely occupy the container, so all gases in the mixture
have the volume of the container
Gas% in Air, by volume
Gas% in Air, by volume
nitrogen, N2 78 argon, Ar 78
oxygen, O2 21 carbon dioxide, CO2 21
Tro's Introductory Chemistry, Chapter
107
Partial Pressure• each gas in the mixture exerts a pressure
independent of the other gases in the mixture
• the pressure of an component gas in a mixture is called a partial pressure
• the sum of the partial pressures of all the gases in a mixture equals the total pressureDalton’s Law of Partial PressuresPtotal = Pgas A + Pgas B + Pgas C +...
atm 1.00 atm 0.01 atm 0.21 atm 0.78 P PP P Ar2O2Nair
Tro's Introductory Chemistry, Chapter
108
Finding Partial Pressure• to find the partial pressure of a
gas, multiply the total pressure of the mixture by the fractional composition of the gas
• for example, in a gas mixture that is 80.0% He and 20.0% Ne that has a total pressure of 1.0 atm, the partial pressure of He would be:
PHe = (0.800)(1.0 atm) = 0.80 atm fractional composition = percentage
divided by 100
Tro's Introductory Chemistry, Chapter
109
Mountain Climbing & Partial Pressure• our bodies are adapted to breathe O2 at
a partial pressure of 0.21 atmSherpa, people native to the Himalaya
mountains, are adapted to the much lower partial pressure of oxygen in their air
• partial pressures of O2 lower than 0.1 atm will lead to hypoxiaunconsciousness or death
• climbers of Mt Everest must carry O2 in cylinders to prevent hypoxiaon top of Mt Everest, Pair = 0.311 atm, so
PO2 = 0.065 atm
Tro's Introductory Chemistry, Chapter
110
Deep Sea Divers & Partial Pressure• its also possible to have too much O2, a condition called oxygen
toxicityPO2 > 1.4 atmoxygen toxicity can lead to muscle spasms, tunnel vision and
convulsions
• its also possible to have too much N2, a condition called nitrogen narcosisalso known as Rapture of the Deep
• when diving deep, the pressure of the air divers breathe increases – so the partial pressure of the oxygen increasesat a depth of 55 m the partial pressure of O2 is 1.4 atmdivers that go below 50 m use a mixture of He and O2 called heliox that
contains a lower percentage of O2 than air
Tro's Introductory Chemistry, Chapter
111
Partial Pressure vs. Total Pressure
At a depth of 30 m, the total pressure of air in the diverslungs, and the partial pressure of all the gases in the air,
are quadrupled!
Tro's Introductory Chemistry, Chapter
112
Collecting Gases• gases are often collected by having them displace
water from a container• the problem is that since water evaporates, there is
also water vapor in the collected gas• the partial pressure of the water vapor, called the
vapor pressure, depends only on the temperature so you can use a table to find out the partial pressure of
the water vapor in the gas you collect
• if you collect a gas sample with a total pressure of 758 mmHg at 25°C, the partial pressure of the water vapor will be 23.8 mmHg – so the partial pressure of the dry gas will be 734 mmHg
Tro's Introductory Chemistry, Chapter
113
Vapor Pressure of WaterTemp., °C Pressure,
mmHg
10 9.2
20 17.5
25 23.8
30 31.8
40 55.3
50 92.5
60 149.4
70 233.7
80 355.1
Tro's Introductory Chemistry, Chapter
114
Zn metal reactswith HCl(aq) toproduce H2(g).
Because waterevaporates, somewater vapor getsmixed in withthe H2.
The gas flowsthrough the tubeand bubbles intothe jar, where itdisplaces the water in the jar.
Tro's Introductory Chemistry, Chapter
115
Reactions Involving Gases• the principles of reaction stoichiometry from
Chapter 8 can be combined with the Gas Laws for reactions involving gases
• in reactions of gases, the amount of a gas is often given as a Volume instead of molesas we’ve seen, must state pressure and temperature
• the Ideal Gas Law allows us to convert from the volume of the gas to moles; then we can use the coefficients in the equation as a mole ratio
Example 11.11:Gases in Chemical Reactions
Tro's Introductory Chemistry, Chapter
117
Example:• How many liters of oxygen gas form when 294 g of
KClO3 completely reacts in the following reaction? Assume the oxygen gas is collected at P = 755 mmHg and T = 308 K
)()()( gss 23 O 3 KCl 2 KClO 2
Tro's Introductory Chemistry, Chapter
118
Example:How many liters of O2(g) form when 294 g of KClO3 completely reacts? Assume the O2(g) is collected at P = 755 mmHg and T = 308 K
• Write down the given quantity and its units.
Given: 294 g KClO3
)()()( gss 23 O 3 KCl 2 KClO 2
K 308 T mmHg, 755 P 2O2O
Tro's Introductory Chemistry, Chapter
119
• Write down the quantity to find and/or its units.
Find:
InformationGiven: 294 g KClO3
PO2 = 755 mmHg, TO2 = 308 K
Example:How many liters of O2(g) form when 294 g of KClO3 completely reacts? Assume the O2(g) is collected at P = 755 mmHg and T = 308 K
)()()( gss 23 O 3 KCl 2 KClO 2
L ,V 2O
Tro's Introductory Chemistry, Chapter
120
• Collect Needed Equation and Conversion Factors:
The relationship between pressure, temperature, number of moles
and volume is the Ideal Gas Law
We also need the molar mass of KClO3 and the mole ratio from
the chemical equation
1 mole KClO3 = 122.5 g KClO3
2 mol KClO3 3 mol O2
nRTPV
InformationGiven: 294 g KClO3
PO2 = 755 mmHg, TO2 = 308 K
Find: VO2, L
Example:How many liters of O2(g) form when 294 g of KClO3 completely reacts? Assume the O2(g) is collected at P = 755 mmHg and T = 308 K
)()()( gss 23 O 3 KCl 2 KClO 2
Tro's Introductory Chemistry, Chapter
121
• Write a Solution Map:
when using the Ideal Gas Equation, the units of V must be L; and the units of P must be atm, or you will have to convert
the units of T must be kelvin, K
InformationGiven: 294 g KClO3
PO2 = 755 mmHg, TO2 = 308 KFind: VO2, LEq’n: PV=nRTCF: 1 mole KClO3 = 122.5 g
2 mole KClO3 3 moles O2
Example:How many liters of O2(g) form when 294 g of KClO3 completely reacts? Assume the O2(g) is collected at P = 755 mmHg and T = 308 K
)()()( gss 23 O 3 KCl 2 KClO 2
nO2 VO2nKClO3g KClO3
3
3
KClO g 5122
KClO mol 1
. 3
2
KClO mol 2
O mol 3
P,T,R
PV=nRT
Tro's Introductory Chemistry, Chapter
122
• Apply the Solution Map: find moles of O2 made
InformationGiven: 294 g KClO3
PO2 = 755 mmHg, TO2 = 308 KFind: VO2, LEq’n: PV=nRTCF: 1 mole KClO3 = 122.5 g
2 mole KClO3 3 moles O2 SM: g → mol KClO3
→ mol O2 → L O2
23
2
3
33 O mol 603
KClO mol 2
O mol 3
KClO g 122.5
KClO mol 1KClO g 294 .
Example:How many liters of O2(g) form when 294 g of KClO3 completely reacts? Assume the O2(g) is collected at P = 755 mmHg and T = 308 K
)()()( gss 23 O 3 KCl 2 KClO 2
Tro's Introductory Chemistry, Chapter
123
• Apply the Solution Map:convert the units
InformationGiven: 294 g KClO3
PO2 = 755 mmHg, TO2 = 308 K, nO2 = 3.60 molesFind: VO2, LEq’n: PV=nRTCF: 1 mole KClO3 = 122.5 g
2 mole KClO3 3 moles O2 SM: g → mol KClO3
→ mol O2 → L O2
atm 423990mmHg 760
atm 1mmHg 557 P .
Example:How many liters of O2(g) form when 294 g of KClO3 completely reacts? Assume the O2(g) is collected at P = 755 mmHg and T = 308 K
)()()( gss 23 O 3 KCl 2 KClO 2
Tro's Introductory Chemistry, Chapter
124
• Apply the Solution Map:
L 90.7 V
atm 423990
K 298 0.0821mol 603 V
P
TRn
TRnVP
Kmol
atmL
.
.
InformationGiven: 294 g KClO3
PO2 = 0.99342 mmHg, TO2 = 308 K, nO2 = 3.60 molesFind: VO2, LEq’n: PV=nRTCF: 1 mole KClO3 = 122.5 g
2 mole KClO3 3 moles O2 SM: g → mol KClO3
→ mol O2 → L O2
Example:How many liters of O2(g) form when 294 g of KClO3 completely reacts? Assume the O2(g) is collected at P = 755 mmHg and T = 308 K
)()()( gss 23 O 3 KCl 2 KClO 2
Tro's Introductory Chemistry, Chapter
125
• Check the Solution:
The units of the answer, L, are correct.It is hard to judge the magnitude with so many variables,but with more than 1 mole of gas at pressures near 1 atm
and temperatures near 273 K – it is reasonable tohave more than 22.4 L
InformationGiven: 294 g KClO3
PO2 = 755 mmHg, TO2 = 308 K, nO2 = 3.60 molesFind: VO2, LEq’n: PV=nRTCF: 1 mole KClO3 = 122.5 g
2 mole KClO3 3 moles O2 SM: g → mol KClO3
→ mol O2 → L O2
Example:How many liters of O2(g) form when 294 g of KClO3 completely reacts? Assume the O2(g) is collected at P = 755 mmHg and T = 308 K
)()()( gss 23 O 3 KCl 2 KClO 2
L 90.7 V2O
Tro's Introductory Chemistry, Chapter
126
Calculate the volume occupied by 1.00 moles of an ideal gas at STP.
• 1 mole of any gas at STP will occupy 22.4 L• this volume is called the molar volume and can
be used as a conversion factoras long as you work at STP
1 mol 22.4 L
(1.00 atm) x V = (1.00 moles)(0.0821 )(273 K)L∙atmmol∙K
V = 22.4 L
P x V = n x R x T
Tro's Introductory Chemistry, Chapter
127
Molar Volume
There is so muchempty spacebetween moleculesin the gas state,the volume of thegas is not effectedby the size of themolecules, (underideal conditions).
Example 11.12:Using Molar Volume
in Calculations
Tro's Introductory Chemistry, Chapter
129
Example:
• How many grams of water will form when 1.24 L of H2 at STP completely reacts with O2?
)()( ggg OH 2 O )(H 2 222
Tro's Introductory Chemistry, Chapter
130
Example:How many grams of water will form when 1.24 L of H2 at STP completely reacts with O2?
• Write down the given quantity and its units.
Given: 1.24 L H2 @ STP
)()( ggg OH 2 O )(H 2 222
Tro's Introductory Chemistry, Chapter
131
• Write down the quantity to find and/or its units.
Find: mass H2O, g
InformationGiven: 1.24 L H2
Example:How many grams of water will form when 1.24 L of H2 at STP completely reacts with O2?
)()( ggg OH 2 O )(H 2 222
132
• Collect Needed Conversion Factors:
We need the molar mass of H2O and the mole ratio from the chemical equation
1 mole H2O = 18.02 g H2O
2 mol H2O 2 mol H2
We also need the molar volume because we are given the
amount of H2 in liters and we are working at STP
1 mol H2 22.4 L
InformationGiven: 1.24 L H2
Find: g H2O
Example:How many grams of water will form when 1.24 L of H2 at STP completely reacts with O2?
)()( ggg OH 2 O )(H 2 222
Tro's Introductory Chemistry, Chapter
133
• Write a Solution Map:
mol H2O g H2Omol H2L H2
2
2
H L 2.42
H mol 1
2
2
H mol 2
OH mol 2
InformationGiven: 1.24 L H2
Find: g H2O
CF: 1 mol H2O = 18.02 g
2 mol H2O 2 mol H2
1 mol H2 22.4 L
Example:How many grams of water will form when 1.24 L of H2 at STP completely reacts with O2?
)()( ggg OH 2 O )(H 2 222
OH mol 1
OH g 0218
2
2.
Tro's Introductory Chemistry, Chapter
134
• Apply the Solution Map:
InformationGiven: 1.24 L H2
Find: g H2O
CF: 1 mol H2O = 18.02 g
2 mol H2O 2 mol H2
1 mol H2 22.4 L
SM: L → mol H2 → mol H2O → g H2O
OH g 9880OH mol 1
OH g 18.02
H mol 2
OH mol 2
H L 22.4
H mol 1H L 1.24 2
2
2
2
2
2
22 .
Example:How many grams of water will form when 1.24 L of H2 at STP completely reacts with O2?
)()( ggg OH 2 O )(H 2 222
Tro's Introductory Chemistry, Chapter
135
• Check the Solution:
The units of the answer, g H2O, are correct.It is hard to judge the magnitude with so many variables,but with less than 22.4 L we have less than 1 mole of H2 -with a mole ratio 2:2 we should expect to make less than
1 mole of H2O
1.24 L H2 = 0.988 g H2O
InformationGiven: 1.24 L H2
Find: g H2O
CF: 1 mol H2O = 18.02 g
2 mol H2O 2 mol H2
1 mol H2 22.4 L
SM: L → mol H2 → mol H2O → g H2O
Example:How many grams of water will form when 1.24 L of H2 at STP completely reacts with O2?
)()( ggg OH 2 O )(H 2 222