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Pressure and Gases

Pressure and Gases. Force per unit area P = F/ A. Pressure. Air is matter, so it has a mass The air’s mass is constantly pushing down on us, so it is exerting a pressure This pressure is very strong. Atmospheric Pressure. An instrument called a barometer is used to measure pressure.

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Pressure and Gases

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  1. Pressure and Gases

  2. Force per unit area • P = F/ A Pressure

  3. Air is matter, so it has a mass • The air’s mass is constantly pushing down on us, so it is exerting a pressure • This pressure is very strong Atmospheric Pressure

  4. An instrument called a barometer is used to measure pressure Measuring Pressure

  5. From a barometer, pressure is measured in mm Hg • Another unit of pressure is the Pascal (Pa)‏ • The most modern pressure unit is the atmosphere (atm)‏ Units of Pressure

  6. Normal pressure at sea level 760 mmHg = 1 atm = 101000 Pa Standard Pressure

  7. How many atm is 800 mm Hg? How many Pa? • How many mm Hg is 3.5 atm? How many Pa? • How many atm is 200000 Pa? How many mm Hg? Converting Pressure Units

  8. 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 Characteristics of Gases

  9. Properties of gases are a result of the fact that the particles are very far apart and move very fast • In air molecules make up only .1% of the volume • In liquid 70% of volume is molecules • Attractive force can exist only in liquids and solids – not in gases Gas Particles

  10. 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. Pressure and the number of molecules are directly related

  11. If you double the number of molecules 1 atm

  12. You double the pressure. 2 atm

  13. As you remove molecules from a container the pressure decreases 4 atm

  14. 2 atm

  15. Until the pressure inside equals the pressure outside • Molecules naturally move from high to low pressure 1 atm

  16. In a smaller container molecules have less room to move. • Hit the sides of the container more often. • As volume decreases pressure increases. Changing the size of the container

  17. Raising the temperature of a gas increases the pressure if the volume is held constant. • The molecules hit the walls harder and more often. Temperature

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