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Behavior of Gases
&Kinetic
Molecular Theory
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
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
Pressure UnitsPressure UnitsPressure UnitsPressure Units
Atmosphere (atm)• Average atmospheric pressure at
sea level at 0oC = 1atm
Torr • Another name for millimeters of
mercury• 1 torr = 1mmHg