This theory helps explain and describe relationships between pressure, volume, temperature, velocity, frequency, and force of collisions. This theory describes the behavior of an ideal gas.

Gas Laws

Kinetic Molecular Theory

• Gases contain particles that are in constant, random, straight line motion.

• Gas particles collide with each other and with the walls of the container. These collisions may result in the transfer of energy among the particles, but there is no loss of energy. The collisions are said to be elastic.

• Gas particles are separated by relatively great distances. Because of this we say that they have no volume.

• Gas particles do not attract each other

What is an Ideal Gas?

• A gas that behaves according to the KMT model is called an IDEAL GAS.

• Hydrogen & Helium are the only gases that act most IDEAL.

• A gas will act most IDEAL when pressure is LOW and temperature is HIGH.

Under Summer Conditons

Deviations• Deviations from the KMT occur

when a gas is under HIGH pressure and has LOW temperature.

• Winter Conditions

Important Terms

Pressure:

Temperature:

Heat:

Is the force exerted by gas particles colliding with the walls of a container.

The measure of a substance’s average kinetic energy.

The amount of energy transferred from one substance to another. Measured in Calories, Joules, or Kilojoules.

How does pressure relate to number of molecules

Pressure and the number of gas molecules are directly proportional

Number of Molecules V.S. Pressure

0102030405060708090

100

1 2 3 4 5 6 7 8 9

Number of Molecules

Pre

ss

ure

Why?

Pressure increases as you add more molecules to a container because there are more molecules to collide with the walls of the container.

Boyle’s LawBoyle’s Law**

P1V1 = P2V2 (T = constant)

Pressure is inversely proportional to volume when temperature is held constant.

A Graph of Boyle’s A Graph of Boyle’s LawLaw

Why?

Pressure will increase when volume is decreased because as you make the area smaller the molecules collide with the walls of the container more frequently.

Gay Lussac’s LawHow are Temperature &

Pressure Related?

•Pressure and Temperature are directly related.

Why? • The molecules hit the walls harder (with more

speed) and more frequently.• Raising the temperature of a gas increases the

pressure if the volume is held constant.

How are Temperature & Pressure Related?

Pressure v.s. Temperature

0

100

200

300

400

500

600

700

1 2 3 4 5 6 7 8 9 10 11

Pressure (Atm)

Te

mp

era

ture

(K

)

Temperature & Volume Charles’ Law

Temperature v.s. Volume

0

20

40

60

80

100

120

1 2 3 4 5 6 7 8 9 10 11

Volume (ml) 10x

Tem

pera

ture

(K)

 The volume of a gas is directly proportional to temperature, and extrapolates to zero at zero Kelvin.

VT

VT

P1

1

2

2 ( constant)

Why?

The volume of a gas expands as temperature increases because the molecules absorb energy and collide with the walls of the container with more force and more frequently.

Temperature and Particle Velocity

Why? As gas particles absorb thermal energy they begin to move around faster.

The Quantity-Volume Relationship: Avogadro’s Law

• Avogadro’s Hypothesis: equal volumes of gas at the same temperature and pressure will contain the same number of molecules (6.02 x 1023).

• Avogadro’s Law: the volume of gas at a given temperature and pressure is directly proportional to the number of moles of gas.

Graham’s Law of Effusion• As kinetic energy increases,

the velocity of the gas molecules increases.

• Effusion is the escape of a gas through a tiny hole (a balloon will deflate over time due to effusion).

• The rate of effusion can be quantified.

Rate of effusion for gas 1Rate of effusion for gas 2

2

1

MM

Distance traveled by gas 1Distance traveled by gas 2

2

1

MM

Effusion:Effusion:

Diffusion:Diffusion:

Graham’s LawGraham’s LawRates of Effusion and DiffusionRates of Effusion and Diffusion

Dalton’s Law of Partial Pressures

For a mixture of gases in a container,

PTotal = P1 + P2 + P3 + . . .

This is particularly useful in calculating the pressure of gases collected over water.

• We can find out the pressure in the fourth container.

• By adding up the pressure in the first 3.

2 atm

1 atm

3 atm

6 atm

Examples

• What is the total pressure in a balloon filled with air if the pressure of the oxygen is 170 torr and the pressure of nitrogen is 620 torr?

• In a second balloon the total pressure is 1.3 atm. What is the pressure of oxygen if the pressure of nitrogen is 0.7 atm?

Examples:Hydrogen gas is added to a 2.00-L flask at a pressure of 5.6 atm. Oxygen gas is added until the total pressure in the flask measures 8.4 atm. What is the mole fraction of hydrogen in the flask?

1.35 moles of argon and 2.75 moles of neon are placed in a 15.0-L tank at 35°C. What is the total pressure in the flask? What is the pressure exerted by neon?

Examples:Hydrogen gas is added to a 2.00-L flask at a pressure of 5.6 atm. Oxygen gas is added until the total pressure in the flask measures 8.4 atm. What is the mole fraction of hydrogen in the flask?

0.67 Partial Press./ Total Press.1.35 moles of argon and 2.75 moles of neon are placed in a 15.0-L tank at 35°C. What is the total pressure in the flask? What is the pressure exerted by neon? Ptot = 6.91 atm

PNe = 4.63 atm