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Aneroid Barometer. How to Measure Pressure. Barometer measures atmospheric pressure. vacuum. P Hg. P atm. Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem. vacuum. mercury (Hg). air pressure. barometer : device to measure air pressure. Empty space (a vacuum).

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how to measure pressure

Aneroid Barometer

How to Measure Pressure

Barometer

  • measures atmospheric pressure

vacuum

PHg

Patm

Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

slide2

vacuum

mercury (Hg)

air

pressure

barometer: device to measure air pressure

barometer

Empty space

(a vacuum)

Hg

Weight of the

mercury in

the column

Weight of the

atmosphere

(atmospheric

pressure)

Barometer

Zumdahl, Zumdahl, DeCoste, World of Chemistry2002, page 401

barometer4
Barometer

Water column

(34.0 ft. high

or 10.4 m)

  • Mercury filled

760 mm = 1 atm

  • Water filled

10400 mm = 1 atm

Atmospheric

pressure

Mercury column

(30.0 in. high

or 76 cm)

The barometer measures

air pressure

barometers
Barometers

Mount Everest

Sea level On top of Mount Everest

Sea level

boiling vs evaporation
Boiling vs. Evaporation

Boiling point: atmospheric pressure = vapor pressure

AIR

PRESSURE

15psi

Revolutionary process - fast

VAPOR

PRESSURE

15 psi

Lyophilization – freeze drying

Evaporation: molecules go from liquid to gas phase

Evolutionary process - slow

gas

liquid

boiling point on mt everest
Boiling Point on Mt. Everest

Water exerts a vapor pressure of 101.3 kPa at

a temperature of 100 oC. This is defined as its

normal boiling point:

‘vapor pressure = atmospheric pressure’

x kPa = 253 mm Hg (101.3 kPa) = 33.7 kPa

(760 mm Hg)

boiling point on mt everest8

On top of Mt. Everest

Boiling Point on Mt. Everest

Water exerts a vapor pressure of 101.3 kPa at

a temperature of 100 oC. This is defined as its

normal boiling point:

‘vapor pressure = atmospheric pressure’

61.3oC

78.4oC

100oC

101.3

93.3

80.0

66.6

chloroform

ethyl alcohol

53.3

Pressure (KPa)

40.0

water

26.7

13.3

0

10

20

30

40

50

60

70

80

90

100

Temperature (oC)

101.3 kPa

x kPa = 253 mm Hg

=

33.7 kPa

760 mm Hg

boiling point on mt everest9
Boiling Point on Mt. Everest

Water exerts a vapor pressure of 101.3 kPa at

a temperature of 100 oC. This is defined as its

normal boiling point:

‘vapor pressure = atmospheric pressure’

61.3oC

78.4oC

100oC

101.3

93.3

80.0

66.6

chloroform

ethylalcohol

Pressure (KPa)

53.3

40.0

water

26.7

13.3

0

10

20

30

40

50

60

70

80

90

100

Temperature (oC)

101.3 kPa

x kPa = 253 mm Hg

=

33.7 kPa

760 mm Hg

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