1. Gas Pressure

2.  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.  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.

4.  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.  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.  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.

7.  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 (1 atm) is equal to 760 mm Hg.

8.  Another unit for pressure uses SI units for force (newtons, N) per area (m 2 ) which is called a Pascal, (Pa).  Under standard conditions, 1 atm of pressure is equal to 101,300 Pa = 101.3 kPa.

9.  Our conversions are: 1.000 atm = 760.0 mm Hg = 101.3 kPa

11. 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 1 = = 760.0 mm Hg 1.000 atm 342 mm Hg 0.450 atm 1 = = 101.3 kPa 1.000 atm 45.6 kPa

12. 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 = = 1.000 atm 760.0 mm Hg 1.13 atm 855 mm Hg 1 = = 101.3 kPa 760.0 mm Hg 114 kPa

13. 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 = = 1.000 atm 101.3 kPa 0.961 atm 97.3 kPa 1 = = 760.0 mm Hg 101.3 kPa 730 mm Hg

14.  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