Gas Laws

Part 1: Kinetic Theory(most of this should be review)

Kinetic Theory of MatterAll matter is moving.Kinetic Energy is the energy of

motion.Temperature is a measure of Kinetic

Energy.Higher temperature indicates more

motion.Motion stops at 0 K (-273˚C)

Kinetics of PhasesSolids the particles have strong Inter-

molecular forces (IMF) with each other but vibrate in place.

Liquids have some IMF but can change position relative to each other.

Gases have very low IMF and have very little interaction with one another.

So...

Solids have a definite shape and volume.

Liquids have definite volume but not definite shape (take the shape of their container)

Gases have no definite shape or volume (expand to fill size and shape of container).

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TemperatureMeasure of the average kinetic energy.

Some particles can be moving very fast.

Some will move very slowly.Most are average.

Vapor Liquid Equilibrium

Stoppered flask, particles cannot escape.

Open beaker they can – eventually will evaporate.

Part II: Properties of Gases

Air Pressure is Due to Gravity

Remember STP?

Standard Air Pressure is measured at Sea Level: 101.3KPa

CompressibilityGas molecules are very smallThe spaces between them are very

largeThe molecules can be forced closer

togetherThey can absorb a lot of energyE.g. car air bags

Intermolecular ForcesThe molecules are randomly moving

very fastThey move in straight-line pathsOnly change direction when they

bump into somethingThe molecules are SO far apart that

the IMF are considered to be zero

Variables in the Gas Formulas

P = pressure in kilopascals (kPa)V = volume of the gas in litres (L)T = temperature in kelvins (K)n = number of moles

Δ Moles, Δ PressureVolume remains constantTemperature remains constantDoubling the number of gas

particles (moles) doubles the pressure

Δ Volume, Δ PressureTemperature remains constantNumber of particles (moles) remains

constantDecreasing the volume by half will

double the pressure

Δ Temperature, Δ PressureVolume remains constant.Number of moles remains constantDoubling the temperature will

double the pressure

Part III: Gas Laws

Boyle’s Law

Temperature remains constantPressure goes up, volume goes

downPressure goes down volume goes up

Inverse relationship creates a curve, not a line…

Charles’s Law

Pressure is constant

Temperature goes up, volume goes up

Temperature goes down, volume goes down.

The Mylar Balloon on a cold day…

Demo

Gay-Lussac’s Law

Volume is constantTemperature increases, pressure

increasesTemperature decreases, pressure

decreases.

Ideal Gas LawPV=nRT where R is the gas law

constant 8.31 L•kPa

Ideal GasesFollow the law preciselyThe particles must have no volumeMust have no IMFNo ideal gases exist

Guess where we find this…

The most ideal gases are H2 and He