Behavior of Gases

&Kinetic

Molecular Theory

Unit 7 – Phase of Unit 7 – Phase of MatterMatter

Characteristic Properties of Characteristic Properties of GasesGasesCharacteristic Properties of Characteristic Properties of GasesGases

Volume – a gas does not have a definite shape or volume. The volume depends on the container size, room temperature and pressure.

Expandability- gases will expand to fit any size container. Increasing temperature will cause the gas to expand thereby increasing volume and pressure in the container.

Characteristic Properties of Characteristic Properties of GasesGasesCharacteristic Properties of Characteristic Properties of GasesGases

Compressibility- the volume of a gas can be decreased by increasing the pressure.

Low Density- because the particles in a gas are so far apart and density is mass per unit volume, it makes sense that gases occupy roughly 1000 times more volume than the same amount of substance as a liquid or solid .

Gases are mostly empty space!

Diffusion and EffusionDiffusion and EffusionDiffusion and EffusionDiffusion and Effusion

Diffusion is the spontaneous mixing of the particles of two different gases.

Effusion is the process where gas particles under pressure will pass through a tiny opening

Graham’s LawGraham’s LawGraham’s LawGraham’s Law

The rate of effusion and diffusion is inversely proportional to the square root of the molar mass of the molecules.

The lower the molar mass, the faster the gas molecules are at a set temperature!

RateA Molar MassB

RateB Molar MassA

=

Graham’s Law of Graham’s Law of Effusion/DiffusionEffusion/DiffusionGraham’s Law of Graham’s Law of Effusion/DiffusionEffusion/Diffusion

Why does reaction “white cloud appear closer to the HCl side?

HCl has a higher molecular weight than NH3 and therefore moves slower!

Kinetic-Molecular TheoryKinetic-Molecular TheoryKinetic-Molecular TheoryKinetic-Molecular Theory

1. Gases consist of tiny particles (atoms or molecules) that are far apart relative to their size.

• The particles have an insignificant volume

2. Gas particles are in constant random motion. They therefore possess kinetickinetic energy defined as KE = ½ (mass)(velocity)2

More energy = faster particles

Kinetic-Molecular TheoryKinetic-Molecular TheoryKinetic-Molecular TheoryKinetic-Molecular Theory

3. There are no forces of attraction or repulsion between the particles.

4. Collisions between gas particles and between particles and the container are elastic. (no net loss of kinetic energy).

Kinetic Molecular TheoryKinetic Molecular TheoryKinetic Molecular TheoryKinetic Molecular Theory

5. The average kinetic energy of gas particles depends on the temperature of the gas.

Higher temperature means more energy and faster particles

PressurePressure PressurePressure

area

forcepressure

Which shoes create the most pressure?

Force = (mass)(acceleration)

PressurePressurePressurePressure

Gas Pressure is created by the collisions of gas particles with a surface.

In general –

more collisions = higher pressure

and less collisions = lower pressure

Units of PressureUnits of PressureUnits of PressureUnits of Pressure

Pascal (Pa)

• 1Pa = 1 newton/m2

Millimeters of Mercury (mmHg)

• Pressure that supports a 1mm mercury column in barometer.

PressurePressurePressurePressure

Barometer• measures atmospheric pressure

Mercury Barometer

in mmHg

Standard Pressure at sea level = 760mmHg

PressurePressurePressurePressure

Manometer• measures contained gas pressure

U-tube Manometer

Pressure UnitsPressure UnitsPressure UnitsPressure Units

Atomosphere (atm)• Average atmospheric pressure at

sea level at 0oC = 1atm

Torr • Another name for millimeters of

mercury• 1 torr = 1mmHg

Pressure UnitsPressure UnitsPressure UnitsPressure Units

KEY UNITS AT SEA LEVEL

1 atm =

760 mm Hg =

760 torr =

101.325 kPa (kilopascal) =

14.7 psi