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2 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

3 Gas Particles Properties of gases are a result of the fact that the particles are very far apart In air molecules make up only.1% of the volume Distance between the particles is 10x as great as the size of the molecules themselves In liquid 70% of volume is molecules Attractive force can exist only in liquids and solids

4 Pressure Force acting over an area P = F/ A Unit - N/ m 2 = Pascal (Pa)

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6 Barometer Instrument used to measure pressure

7 Standard Atmospheric Pressure 760 mm Hg = 760 torr = kPa Another unit of pressure The atmosphere (atm) 1 atm = 760 torr

8 Convert.650 atm = ____________mmHg 3.5 x 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

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 K and heat it to 600 K one of 2 things happens 300 K

Either the volume will increase to 2 liters at 1 atm 300 K 600 K

300 K 600 K Or the pressure will increase to 2 atm. Or someplace in between