Gases
Physical Characteristics &
Molecular Composition
Chapter 10 & 11
Kinetic- Molecular Theory of Gases
•
•
Describes the behavior of matter
Based on Five Assumptions:
1) Gases consist of large numbers of tiny particles that are far
apart
2) Collisions with other particles and container are elastic. (No loss
of energy)
3) Gas particles are in constant, rapid motion
4) No forces of attraction/repulsion between gas
particles
5) Average kinetic energy is dependent on
temperature
•
•
Ideal Gases: Meet all the requirements of
the K-M Theory
No such thing as an ideal gas – a gas
may behave nearly ideally under lower
pressure and higher temps. – when gas
particles are far apart
Properties of Gases
•
No definite volume or shape
•
Completely fill their container
Assump. #1 Gases consist of large numbers of tiny particles that
are far apart
•
Low density compared to the same substance in liquid or solid
state
•
Can be compressed
Properties of Gases- cont.
Assump #3- Gas particles are in constant,
rapid motion
• Diffusion- spontaneous mixing of particles
caused by random motion
Assump #4- No forces of attraction/repulsion
between gas particles
• Very fluid- gas particles “glide” past each other
Section 10-2
•
Four Quantities to Describe Gases
1)
2)
3)
4)
Volume (L)
Number of Molecules (moles)
Temperature (K= Kelvin= °C + 273)
Pressure (atm)
Pressure
• Pressure: force per unit area on a surface
• Pressure: force
area
• Gas molecules will exert pressure as a
result of collisions with walls of container
or surface
• STP = standard temperature and pressure
standard temp = 0 C
standard pressure = 1 atm
Conversions with Pressure
•
•
•
•
1 mm Hg = 1 torr
1 atm= 760 mm Hg
1 atm= 760 torr
1 atm = 101.325 kPa
Example 1
•
The average atmospheric pressure in
Denver, Colorado, is 0.830 atm.
A) Convert this to mm Hg
B) Convert this to kPa
Example 2
• Convert 570 torr into mmHg and atm.
Convert 125 mm Hg into atm
A.
B.
C.
D.
0.164 atm
0.725 atm
1.271 atm
30. 26 atm
Convert 3.20 atm into kPa
A.
B.
C.
D.
74.63 kPa
862.00 kPa
6391.45 kPa
324.2 kPa
Convert 5.38 kPa into torr
A.
B.
C.
D.
15.5 torr
40.4 torr
57.8 torr
82.1 torr
Four Quantities to Describe Gases
1)
2)
3)
4)
-
Volume (L)
Number of Molecules (moles)
Temperature (K= Kelvin= °C + 273)
Pressure (atm)
Each quantity is affected by a change in
another
Ideal Gas Law: PV=nRT
Chapter 10- Section 3
The Gas Laws
Gay- Lussac’s & Boyle’s
Laws(pg. 23)
• Objectives:
• Use the K-M theory to explain the relationships
between gas volume, temperature, and
pressure.
• Use Boyle’s Law to calculate volume-pressure
changes at a constant temperature
• Use Gay-Lussac’s Law to calculate pressuretemperature changes at a constant volume
Gay-Lussac’s Law
• When we increase the temperature of a gas,
the gas, particles speed up.
• When the gas particles speed up, what
happens to the number of collisions of the
particles?
• What happens to the pressure inside a
closed container?
•  Temperature,  Pressure
• P  T Pressure is directly proportional to temperature
Gay-Lussac’s Law
• We can use this relationship to determine
how changing one variable will affect the
others
• PT
• Gay-Lussac’s Equation
P1
T1
P2
T2
Temperature must be in Kelvins!
K = C + 273
17 C = _________K
Example 1
• The gas in an aerosol is at a pressure of 3.00 atm at
25 °C. Directions on the can warn the user to not keep the can in a
place where the temperature exceeds 52 °C. What would the
pressure be in the can at 52 °C?
Example 2
• Before a trip from New York to Boston, the pressure in a
automobile tire is 1.8 atm at 20° C. At the end of the trip,
the pressure gauge reads 1.9 atm. What is the new
temperature inside the tire?
Boyle’s Law
• When we decrease the size of the container,
what happens to the number of collisions of
the gas particles?
• What happens to the pressure inside the
container?
•  Volume,  Pressure
• P  1 Pressure is indirectly proportional to volume
V
Boyle’s Law- Volume & Pressure
• We can use this relationship to
determine how changing one variable
will affect the others
• P1V1= P2V2
Example 3
• A sample of oxygen gas has a volume of 150 mL
when its 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?
Example 4
• A gas has a pressure of 1.26 atm and occupies a volume
of 7.40 L. If the gas is compressed to a volume of 2.93
L, what will its pressure be?
Charles’ Law (Pg. 25)
Objectives:
• Use Charles’ Law to calculate volumetemperature changes at a constant
pressure
Charles’ Law- Volume and
Temperature
• If we increase temperature, what
happens to the speed of the gas
molecules?
• What happens to the volume of a
flexible container?
•  Temperature,  Volume
• V  T Volume is directly proportional to temperature
Charles’ Law- Volume and
Temperature
• V1= V2
T1 T2
• Temperature must be in Kelvins!
Example 5
• 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?
Combined Gas Laws
• In reality, more than one variable changes
at a time. Therefore, if we combine the
Gas Laws, we can measure the effect of
changing several variables.
• Combined Gas Law: P1V1 = P2V2
T1
T2
• Temperatures must be in Kelvins!
Example 7
• A helium filled balloon has a volume of 50 L at
25 °C and 1.08 atm. What volume will it have at
0.855 atm and 0 °C ?
Dalton’s Law of Partial Pressure
• Pt = P1 + P2 + P3 + …
• The total pressure of a mixture of gases is
equal to the sum of the partial pressures of
the component gases.
Dalton’s Law of Partial Pressure
• A sealed container of gases consist of
carbon dioxide, water vapor, and oxygen
at 5.9 atm. If oxygen has a partial
pressure of 1.4 atm and carbon dioxide
has a partial pressure of 3.6 atm, what is
the partial pressure of water vapor?
Bellwork Tuesday2/24 (pg. 18)
• A helium filled balloon has a volume of 2.75 L at 20
°C. The volume of the balloon decreases to 2.46 L
after it is placed outside on a cold day. What is the
outside temperature in Kelvin? In Celsius?
Avogadro’s Law and Combined
Gas Law (pg. 27)
• Objective:
– To understand the relationship between
number of molecules and pressure
– Use the combined gas law to calculate
volume temperature-pressure changes
What is STP???
• STP: Standard Temperature and Pressure
• STP: Temperature: 0°C= 273 K
Pressure: 1 atm
Avogadro’s Law
• Standard molar volume of a gas- The
volume occupied by one mole of gas at
STP
• At STP, 1 mol= 22.41 L
Ideal Gas Law
• What happens to the number of collisions of
gas molecules when you decrease the
number of molecules?
• What happens to the pressure?
•  Number of molecules,  Pressure
• P  n Pressure is directly proportional to # of molecules
Ideal Gas Law
• Mathematical relationship among
pressure, volume, temperature, and
number of moles of a gas
• PV=nRT
• R= Ideal Gas Constant= 0.0821 L*atm
mol*K
n = number of moles
A 2.07 L cylinder contains 2.88 mol of
helium gas at 22°C. What is the pressure of
the gas in the cylinder?
A. 36.7 atm
]
B. 6.5 atm
C. 33.7 atm
D. 16.9 atm
What is the volume of 0.250 mol of
oxygen gas at 20.0 C and 0.974
atm?
A. 9.6 L
B. 6.2 L
C. 23.2 L
D. 3.9 L
A sample of 0.073 mol of carbon dioxide
was placed in a 250mL container at 400K.
What was the pressure exerted by the gas?
A. 9.6 atm
B. 0.01 atm
C. 1.8 atm
D. 0.54 atm
Convert 0.470 atm to mmHg.
A. 16.9 mmHg
B. 433.0 mmHg
C. 219.3 mmHg
D. 357.2 mmHg
At a pressure of 780.0 mmHg and 24.2 C, a
certain gas has a volume of 350.0 ml. What
will be the volume of this gas at STP?
A. 65.4 ml
B. 330.0 ml
C. 250,770.5 ml
D. 5,449.0 ml
A sample of argon has a volume of 0.43ml
at 24C. At what temperature in degrees
Celsius will it have a volume of 0.57ml?
A. 121 C
B. 394 C
C. 32 C
D. 215 C
A sample of an unknown gas has a mass of
0.116g. It occupies a volume of 2.5L at a
temperature of 27C and a pressure of 725mmHg.
Calculate the molar mass of the gas.
A. 73.6 g/mol
B. 0.836 g/mol
C. 1.2 g/mol
D. 13.5 g/mol
What is the molar mass of a gas if
0.427g of the gas occupies a volume of
0.125L at 20C and 0.980atm?
A. 57.5 g/mol
B. 15.4 g/mol
C. 0.01 g/mol
D. 85.4 g/mol
A student collected 0.425L of oxygen (O2) at a
temperature of 24C and a pressure of
683.2mmHg. What is the mass of the oxygen
collected?
A. 3.244g
B. 0.512g
C. 1.523g
D. 112.9g
• A 4.00g sample of O2 at 57 C has a
pressure of 674.88mmHg. What is the
volume of this gas?
• A reaction produces 375ml of nitrogen
monoxide at 19 C and a pressure of
1.10atm. What mass of NO was produced
by the reaction?