Gases
An Exploration in Ideal Gas Behavior
Loosely adapted from: Philip Dutton University of Windsor, Canada and Martin Silberberg
Some Important Industrial Gases
Name (Formula)
Origin and use
Methane (CH4)
Natural deposits; domestic fuel
Ammonia (NH3)
From N2 + H2 ; fertilizers, explosives
Chlorine (Cl2)
Electrolysis of seawater; bleaching
and disinfecting
Oxygen (O2)
Liquified air; steelmaking
Ethylene (C2H4)
High-temperature decomposition of
natural gas; plastics
Substances That Are Gases under
Normal Conditions
Substance
Helium
Neon
Argon
Hydrogen
Nitrogen
Nitrogen monoxide
Oxygen
Hydrogen chloride
Ozone
Ammonia
Methane
Formula
MM(g/mol)
He
Ne
Ar
H2
N2
NO
O2
HCl
O3
NH3
CH4
4.0
20.2
39.9
2.0
28.0
30.0
32.0
36.5
48.0
17.0
16.0
The Three Common States of Matter
Important Characteristics of Gases
1) Gases are highly compressible
An external force compresses the gas sample and decreases its
volume; removing the external force allows the gas volume to
increase.
2) Gases are thermally expandable
When a gas sample is heated, its volume increases; when it is
cooled its volume decreases.
3) Gases have low viscosity
Gases flow more easily than liquids or solids.
Important Characteristics of Gases
4) Most Gases have low densities
Gas densities are on the order of grams per liter whereas
liquids and solids are grams per cubic cm, 1000 times greater.
5) Gases are infinitely miscible
Gases mix in any proportion. An example of such is air, a
mixture of many gases.
Properties of Gases: Gas Pressure
• Gas Pressure
Force (N)
P (Pa) =
Area (m2)
Pressure of the Atmosphere
• Called “atmospheric pressure,” or the force exerted upon us by the
atmosphere above us.
A measure of the weight of the atmosphere pressing down upon us.
Pressure =
Force
Area
• Measured using a barometer - A device that can “weigh” the atmosphere
above us.
A Mercury Barometer
Effect of Atmospheric Pressure on
Objects at the Earth’s Surface
Common Units of Pressure
Unit
Atmospheric Pressure
Scientific Field
pascal (Pa);
kilopascal(kPa)
1.01325 x 105 Pa
101.325 kPa
SI unit; physics,
chemistry
atmosphere (atm)
1 atm*
Chemistry
millimeters of mercury
( mm Hg )
760 mmHg*
Chemistry, medicine,
biology
torr
760 torr*
Chemistry
pounds per square inch 14.7 lb/in2
( psi or lb/in2 )
Engineering
bar
Meteorology, biology
chemistry, physics
1.01325 bar
Converting Units of Pressure
Problem: A chemist collects a sample of carbon dioxide from the
decomposition of limestone (CaCO3) in a closed end manometer, the
height of the mercury is 341.6 mm Hg. Calculate the CO2 pressure in
torr, atmospheres, and kilopascals.
Solution:
converting from mmHg to torr:
PCO2 (torr) = 341.6 mm Hg x
1 torr
= 341.6 torr
1 mm Hg
converting from torr to atm:
1 atm = 0.4495 atm
PCO2( atm) = 341.6 torr x
760 torr
converting from atm to kPa:
PCO2(kPa) = 0.4495 atm x 101.325 kPa = 45.54 kPa
1 atm
Characterization of a Gas Sample
To fully characterize any gas sample, 4
variables must be accounted for:
Pressure (P)
Volume (V)
Quantity of gas in moles (n)
Kelvin Temperature (T)
Experiment this week
Determine the relationship between:
P and V
P and T
Vernier Pressure Sensor
Note:ofPressure
mustPlease
not exceed
kPa. Start with
Lots
little parts.
don’t220
lose
syringe
compress
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further than 5
them.
Use ata 10
60 mL
mLand
syringe
rather
Draw
plungerin
back
get larger volumes.
themL.
20 mL
supplied
thetobox.
Set up LoggerPro to collect data on command:
Experiment | Data Collection
Attach syringe
to Leur-lock with a gentle
Change Mode: Events with Entry
push…
…then
gentle twist.
doesn’t have to
A Note
onaPressure
VersusItTemperature:
be What
reallymust
tight.
it doesn’t.
beReally,
constant?
Use a small Erlenmeyer flask and the plastic
tubing to attach the sensor. Clamp the flask
below the surface of water in a big beaker.
Use ice for subambient temperatures. Heat to
no hotter than about 80°C
Other Notes
The thermometers don’t know how to swim!
– Please don’t teach them
Show P-V and P-T plots to TA/Instructor before
leaving lab
No proposal this week:
– Measure pressure at many volumes
– Assemble a closed system and study pressure with
changing temperature.
Other Notes
This investigation, Author
2: Introduction and Conclusion
3: Discussion
1: Data/Results and Experimental
This investigation, Author
B: Introduction, Conclusion, Data/Results
A: Discussion and Experimental