Gas Laws
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Gas Laws
The Kinetic Molecular Theory
• Gas particles do not repel or attract each other.• Gas particles are much smaller than the
distances between them.• Gas particles are in constant, random motion.• No kinetic energy is lost when gas particles
collide.• All gases have the same kinetic energy at a
given temperature.
Pressure
• Pressure is force applied over an area.• For gases, the pressure is determined by the
number of collisions with the walls of the container.
• Units: – atm: atmospheres– kPa: kiloPascal (= 1 N/m2)– mmHg: millimeters of mercury– psi: pound force per square inch
The variables and their units
Variable Symbol Units
Pressure P atm
Volume V Liters
Amount of gas n Moles
Temperature T Kelvin
Conversion Factors
Conversion for Pressure
1 Torr = 1 mm Hg
Conversion Factors
Conversion for Temperature
STP
The Relationships
Copy in color: 10 x 4 = 8 x ??
• What is the missing number?
• From before to after:– How did the red number change?
– How did the black number change?
• What is the math term for this relationship?
• Which two gas variables have this type of relationship?
before after
The Relationships
Inversely proportional 10 x 4 = 8 x ??
Pressure and volume
P1V1 = P2V2
The Relationships
Copy in color: ? 166 48
• What is the missing number?
• From before to after:– How did the red number change?
– How did the black number change?
• What is the math term for this relationship?
• Which two gas variables have this type of relationship?
=
before after
The RelationshipsDirectly proportional ? 16
6 48
Pressure and Temperature
Volume and Temperature
Volume and amount of gas
=
2
2
1
1
T
P
T
P
2
2
1
1
T
V
T
V
2
2
1
1
n
V
n
V
The Combined Gas Lawif every gas variable changed, this is the relationship
22
22
11
11
Tn
VP
Tn
VP
Things that don’t change can cancel or drop out.
The Combined Gas Lawif every gas variable changed, this is the relationship
22
22
11
11
Tn
VP
Tn
VP
If amount of gas and volume stay the same, they cancel or drop out.
2
2
1
1
T
P
T
PSimplifies to
The Combined Gas Lawif every gas variable changed, this is the relationship
22
22
11
11
Tn
VP
Tn
VP
If amount of gas and temperature stay the same, they cancel or drop out.
Simplifies to P1V1 = P2V2
Let’s PracticeAt 20°C, the volume of a gas is 100.0 mL.
The temperature is raised to 100°C.
How do you expect the volume to change?
It should increase
Simplify the Combined Gas Law for this scenario.
T1 V1
T2
22
22
11
11
Tn
VP
Tn
VP
2
2
1
1
T
V
T
VSimplifies to
Let’s PracticeAt 20°C, the volume of a gas is 100.0 mL.
The temperature is raised to 100°C.
T1 V1
T2
2
2
1
1
T
V
T
V
+273 = 293K
+273 = 373K
V2 = 127 mL
Does this match your prediction? You said
it would increase.
Let’s Practice50.0 mL of a gas has a pressure of 740.0 mmHg when
it is in a container.
The pressure changes to 760.0 mmHg. How do you expect the volume to change?
It should decreaseSimplify the Combined Gas Law for this scenario.
V1 P1
P2
22
22
11
11
Tn
VP
Tn
VP Simplifies to P1V1 = P2V2
Let’s Practice50.0 mL of a gas has a pressure of 740.0 mmHg when
it is in a container.
The pressure changes to 760.0 mmHg?
V1 P1
P2
P1V1 = P2V2
(740.0mmHg)(50.0mL) = (760.0mmHg)V2
48.7 mL = V2Does this match your prediction? You said it
would increase.
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