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Characteristics of Gases
Vapor – substance ordinarily a liquid or solid but in its gaseous phase
Gas expands to fill its container
Highly compressible when pressure is applied – liquids and solids not
Form homogeneous mixtures
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Gas Particles
Properties of gases are a result of the fact that the particles are very far apartIn air molecules make up only .1% of the volumeDistance between the particles is 10x as great as the size of the molecules themselvesIn liquid 70% of volume is moleculesAttractive force can exist only in liquids and solids
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Pressure
Force acting over an area
P = F/ A
Unit - N/ m2 = Pascal (Pa)
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Barometer
Instrument used to measure pressure
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Standard Atmospheric Pressure
760 mm Hg = 760 torr = 101.325 kPa
Another unit of pressureThe atmosphere (atm)1 atm = 760 torr
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Convert
.650 atm = ____________mmHg
3.5 x 10-4 mm Hg = ___________atm
735 mm Hg = _____________kPa
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Pressure and the number of molecules are directly
related More molecules means more collisions.
Fewer molecules means fewer collisions.
Gases naturally move from areas of high pressure to low pressure because there is empty space to move in.
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1 atm
If you double the number of molecules
If you double the number of molecules
You double the pressure.
2 atm
As you remove molecules from a container
4 atm
As you remove molecules from a container the pressure decreases
2 atm
As you remove molecules from a container the pressure decreases
Until the pressure inside equals the pressure outside
Molecules naturally move from high to low pressure
1 atm
Changing the size of the container
In a smaller container molecules have less room to move.
Hit the sides of the container more often.
As volume decreases pressure increases.
1 atm
4 Liters
As the pressure on a gas increases
2 atm
2 Liters
As the pressure on a gas increases the volume decreases
Pressure and volume are inversely related
Temperature
Raising the temperature of a gas increases the pressure if the volume is held constant.The molecules hit the walls harder.The only way to increase the temperature at constant pressure is to increase the volume.
If you start with 1 liter of gas at 1 atm pressure and 300 Kand heat it to 600 K one of 2 things happens
300 K
Either the volume will increase to 2 liters at 1 atm
300 K600 K
300 K 600 K
•Or the pressure will increase to 2 atm.•Or someplace in between