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The Nature of Gases - Part 2

The Nature of Gases - Part 2. Gas Pressure. 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.

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The Nature of Gases - Part 2

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  1. The Nature of Gases - Part 2 • Gas Pressure

  2. 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 vacuum is a volume where there are no gas molecules bouncing off a surface. Atmospheric pressure results from the collision of air molecules with objects.

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

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

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

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

  9. 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.

  10. Pressure Units Our conversions are: 1.000 atm = 760.0 mmHg = 101.3 kPa

  11. Let’s do some examples

  12. 101.3 kPa 760.0 mm Hg 0.450 atm 0.450 atm 1 atm 1 atm 1 1 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: × = 342 mm Hg × = 45.6 kPa

  13. 101.3 kPa 855 mm Hg 1 atm 855 mm Hg 760 mm Hg 760 mm Hg 1 1 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: × = 1.13 atm × = 114 kPa

  14. 760 mm Hg 97.3 kPa 97.3 kPa 1 atm 101.3 kPa 101.3 kPa 1 1 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: × = 0.961 atm × = 730 mm Hg

  15. 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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