PRESSURE

1
PRESSURE

• 10-2

2
How much gas is in your outdoor grill propane
tank?
3
To describe the amount of gas you have, what 4
measurable quantities do you need?

• volume
• temperature
• particles
• pressure

4
PRESSURE

• force per unit area of a surface
• P force
• area
• SI unit for force is the newton force that will
  increase the speed of one kilogram mass by 1m/s
  every second

5
Where is the pressure the greatest?
6
Useful pressure units
7
Equivalent pressure units

• At sea level, the average atmospheric pressure
  is..
• 1 atmosphere (atm) (exact )
• 760 mm Hg (exact )
• 760 torr (exact )
• 101.325 kilopascals (kPa)
• 29.9 inches of Hg
• 14.7 psi (lbs/inch2)

8
Showing known, unknown and conversion info, use
FLM to perform the following conversions

• 795 mm to kPa
• 921 torr to atm
• 121.4 kPa to mm Hg
• 441 mm Hg to atm

9
Torricelli discovered that the pressure of the
atmosphere supports a column of Hg about 760 mm
above a dish of Hg
10
What instrument is used to measure gas pressure?

• Manometer
• barometer manometers used to measure atmospheric
  pressure
• sphygmomanometer manometer used to measure blood
  pressure

11
Closed-tube manometer
What is the pressure (kPa) of the gas in the
manometer if the height of the column of mercury
in the long arm is 25 mm greater than the height
of mercury in the short arm?
12
25 mm
25 mm Hg x 101.325 kPa 3.3 kPa
760 mm Hg
13
Open-tube Manometers used to measure pressures
that are close to atmospheric pressure
14
If the atmospheric P is 99.8 kPa, what is the
pressure?
55 mm
15
What is the pressure of the gas if the
atmospheric pressure is 102.3 kPa and the height
of the Hg column is 42 mm higher in the gas
sample arm?
16
102.3 kPa
42 mm
17
STP

• standard temperature and pressure
• needed for comparisons
• standard temperature 00C
• standard pressure 1 atm (exact)