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The Nature of Gases – Part 2

Gas Pressure. The Nature of Gases – Part 2. Objectives. When you complete this presentation, you will be able to: describe gas pressure in terms of the motion of gas particles. describe the invention of the barometer. describe the derivation of the units of pressure.

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The Nature of Gases – Part 2

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  1. Gas Pressure The Nature of Gases – Part 2

  2. Objectives • When you complete this presentation, you will be able to: • describe gas pressure in terms of the motion of gas particles. • describe the invention of the barometer. • describe the derivation of the units of pressure. • convert between the units of pressure.

  3. Introduction • Gas pressure is the result of the force of gas molecules exerted on a surface. • The force of a single molecule of gas in insignificant, but the force of trillions of molecules becomes measurable. • A vacuumis a volume where there are no gas molecules bouncing off a surface. • Atmospheric pressure results from the collision of air molecules with objects.

  4. Measuring Pressure • We measure the pressure of a gas by using an instrument called a barometer. • The barometer was invented in 1643by the Italian physicist Evangelista Torricelli. • He made a barometer from a tube of glass (sealed at one end) and a trough of mercury.

  5. Measuring Pressure • We measure the pressure of a gas by using an instrument called a barometer. • The barometer was invented in 1643by the Italian physicist Evangelista Torricelli. • He made a barometer from a tube of glass (sealed at one end) and a trough of mercury.

  6. Measuring Pressure • We measure the pressure of a gas by using an instrument called a barometer. • The barometer was invented in 1643by the Italian physicist Evangelista Torricelli. • He made a barometer from a tube of glass (sealed at one end) and a trough of mercury. • The airpressure on the Hg held the column up.

  7. Pressure Units • The air pressure in a barometer is measured by measuring the heightof the mercury column. • Under standard conditions, a column of mercury will be 760 mmin height. • So, we say that 1 atmosphere of pressure (1 atm) is equal to 760 mm Hg.

  8. Pressure Units • Another unit for pressure uses SI units for force (newtons, N) per area (m2) which is called a Pascal, (Pa). • Under standard conditions, 1 atm of pressure is equal to 101,300 Pa = 101.3 kPa.

  9. Pressure Units • Our conversions are: 1.000atm = 760.0 mm Hg = 101.3 kPa

  10. Let’s do some examples

  11. Example 1 A container of oxygen gas has a pressure of 0.450 atm. Find the pressure in mm Hg and kPa. Conversions: 1.000 atm = 760.0 mm Hg = 101.3 kPa Solution: 0.450 atm 760.0 mm Hg 101.3 kPa 342 mm Hg = = = 1.000 atm 1.000 atm 1 1 0.450 atm 45.6 kPa =

  12. Example 2 A container of nitrogen gas has a pressure of 855 mm Hg. Find the pressure in atm and kPa. Conversions: 1.000 atm = 760.0 mm Hg = 101.3 kPa Solution: 855 mm Hg 1.000 atm 101.3 kPa 1.13 atm = = = 760.0 mm Hg 760.0 mm Hg 1 1 855 mm Hg 114 kPa =

  13. Example 3 A container of hydrogen gas has a pressure of 97.3 kPa. Find the pressure in atm and mm Hg. Conversions: 1.000 atm = 760.0 mm Hg = 101.3 kPa Solution: 97.3 kPa 1.000 atm 760.0 mm Hg 0.961 atm = = = 1 1 101.3 kPa 101.3 kPa 97.3 kPa 730 mm Hg =

  14. Summary • Gas pressure is the result of the force of gas molecules exerted on a surface. • Atmospheric pressure results from the collision of air molecules with objects. • We measure the pressure of a gas by using an instrument called a barometer invented in 1643 by the Italian physicist Evangelista Torricelli. • Our conversions are: 1.000 atm = 760.0 mmHg = 101.3 kPa

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