Date post: | 30-Dec-2015 |
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Objectives
1. Define pressure and relate it to force
2. Describe how pressure is measured.
3. Convert units of pressure.
4. State the standard conditions of temperature and pressure.
Pressure
To adequately describe a gas, you must know…• Volume• Temperature• Number of particles• Pressure
area
force Pressure
Atmospheric PressureThe gases that make up the
atmosphere exert pressure on their surroundings. It is a result of:
1. Collisions between gas particles.
2. The weight of the atmospheric gases above the earth’s surface.
Measuring Pressure • Atmospheric pressure is
measured using a barometer.
• Atmospheric pressure depends on elevation and weather.
• Normal atmospheric pressure at sea level: 760 mm Hg
Measuring Pressure• A manometer can be
used to measure the pressure of an enclosed gas.
• The pressure is measured relative to atmospheric pressure.
Units of PressureUnit Symbol Std. Atmospheric
pressure
Millimeters of Hg mm Hg 760
Centimeters of Hg cm Hg 76
Inches of Hg in. Hg 29.92
Torr Torr 760
Pascals (N/m2) Pa 101,325
Atmospheres atm 1
Pounds per square inch psi 14.69
bars bar 1.01325
•The Pascal is the SI unit
Pressure Conversions• Convert 35 psi into units of atmospheres.atm
psi1
35 atm
psi
atmpsi 4.2
69.14
135