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.