Honors ChemChapters 10, 11, and 12

Kinetic Molecular Theory (KMT)Molecules are constantly in motion and

collide with one another and the wall of a containerParticles move faster with increased

temperatureGases are made of mostly empty space and just

a few fast moving particles.

Properties of GasesLow DensityExpansionCompressibility FluidityDiffusion/Effusion

Nature of GasesDiffusion: spontaneous mixing of gases

Nature of GasesEffusion: gas particles

spontaneously pass through a small opening

Graham’s Law of Diffusion (or Effusion)

Smaller, lighter gas molecules move faster through the air than larger, heavier gas molecules.

“Lighter, faster, farther”

Graham’s Law of Diffusion (or Effusion)

Graham’s Law: Rewrittenr = rate MM= Molar Mass d = distance t = time light = lighter gas heavy = heavy gas

Kinetic Molecular Theory (KMT)Molecules are constantly in motion and

collide with one another and the wall of a containerParticles move faster with increased

temperatureGases are made of mostly empty space and just

a few fast moving particles.

Ideal GasIdeal Gas: a gas that perfectly conforms to

assumed gas behavior (doesn’t exist)

Most gases are described using real conditions and variables

Variables of Gases(P) Pressure

(V) Volume

(T) Temperature

(n) Amount of gas in moles

PressureMeasures: Force exerted by moving gas particle collisions with their container

Pressure UnitsUnits: 1 atm (atmosphere) of pressure is the

average pressure at sea level

Important Conversions: 1 atm = 760 mmHg (millimeters of Mercury)

= 760 torr= 101.3 kPa (kilo Pascals)= 14.7 psi (pounds per square

inch)

VolumeMeasures: amount of space that a gas

occupies

Units: Liters (L)

Important Conversions: 1 L = 1000mL

TemperatureMeasures: average kinetic energy of gas

particles.

Units: Kelvin (K)The Celsius scale is NOT used for gases

because gases can still have kinetic energy at negative and 0o C.

Kelvin Scale and Absolute ZeroAbsolute Zero = 0 Kelvin represents the

temperature at which a gas has NO kinetic energy

Converting TemperatureImportant Conversions:

oC + 273 = K

K – 273 = oC

STPSTP = Standard Temperature and Pressure

Exactly 0oC and 1 atm

At STP, one mole of gas (6.02 x1023 particles)occupies 22.4 L If a gas is not held at STP, then volume is

recalculated

Gas VariablesA variable is a factor that is liable to change.

Pressure, temperature, and volume of a gas are liable to change.

Pressure, volume, and temperature are interdependent. When variable changes, they all do.

The Combined Gas Law Relates pressure, temperature, volume, and

moles of a gas Relates initial and final conditionsVariables that do not change are constants

and not included in the equation

The Combined Gas Law Equation

The left side (1) represents the initial conditions of the gas

The right side (2) represents the final conditions of the gas

Charles’ Law: Volume and Temp

What changes? And How?Volume increases, temperature increases

What stays the same? Pressure and moles are held constant (toss ‘em)

Charles’ Law: Equation

Remember: Temperatures must be in Kelvin

2

2

1

1

T

V

T

V

Charles’ Law: GraphDirect Relationship: both variables increase

together

Charles Law: Simulation

Charles’ Law: Video Demo

Charles’ Law : ExampleA gas sample at 25 oC and 752 mL is heated

to 50 oC, what is the new volume?

Boyle’s Law : Pressure and Volume

What changes? And How? When Pressure increases, Volume decreases

What stays the same? Temperature and moles are held constant (toss

‘em)

Boyle’s Law : Equation

Remember: Pressure units on both sides of the equation must be the same

P1V1 = P2V2

Boyle’s Law: GraphInverse Relationship: an increase in one

variable with a simultaneous decrease in the other

Boyle’s Law: Simulation

Boyle’s Law: Video Clip

Boyle’s Law ExampleQ: A 1.0 L sample of gas is held at standard

pressure, 1.0 atm. The pressure of the gas is reset to 152 mmHg. What is the new volume of the gas?

Gay-Lussac’s Law: Pressure and Temperature

What changes? And how? As temperature of a gas increases, the pressure

also increasesWhat stays the same?

Volume and moles are held constant (toss ‘em)

Gay-Lussac’s Law: Equation

Pressure units on both sides of the equation must be the same

Temperature must be in Kelvin

2

2

1

1

T

P

T

P

Gay-Lussac’s Law: GraphDirect Relationship: Both variables increase

together

Gay-Lussac’s Law: Simulation

Gay-Lussac’s Law: Video Clip

Gay-Lussac’s Law: Example

Q: A gas has a pressure of 0.370 atm at 50.0 °C. What is the pressure at standard temperature?