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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