10/21/2014
Behavior & Properties of Gases
Gas Laws & Applications

Today:
◦ Composition and Pressure of
the Atmosphere
 Units for measuring pressure
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◦
◦
◦

Next Monday in Lab: Turn
in Post Lab Questions for
Experiments 4 & 5
Boyle’s Law
Charles’ Law
Gay Lussac Law
Combined Gas Law
Introduction to Gases:



Gas is all around us
The air is mostly
N 2 & O2
Gases consist of many particles in constant, straightline, random motion
◦ COLLISIONS of gaseous particles on surfaces exert
tiny forces which ADD UP to observable PRESSURE
At room temperature: gaseous
Helium atoms travel with an average
velocity of ~3,000 mph while N2 has
an average velocity of~1,000 mph
Jan Baptista van Helmont (1577-1644) named gases after the
Greek word, “chaos” but spelled it in accordance with its
phonetic sound in Flemish, which made it “gas.”
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10/21/2014
Gaseous particles DO NOT INTERACT strongly with their
neighbors
(in comparison to the thermal energy of the environment)

The average kinetic energy (energy due to motion) is
proportional to the temperature of the gas (in Kelvins)
• As the gas particles become heavier, they move more slowly
• As temperature goes up, gases move faster.


We live under a sea of gas called the ATMOSPHERE
The atmosphere extends roughly
62 miles above sea level, but
with 75% of the mass occurring
within the first 6.8 miles from
the surface
Pressure =
𝑭𝒐𝒓𝒄𝒆
𝑨𝒓𝒆𝒂
At sea level, the
weight of the
atmosphere exerts
a PRESSURE equal
to 14.7 pounds per
square inch (psi) or
1 atm
Pressure =
Large Area → Low Pressure
𝑭𝒐𝒓𝒄𝒆
𝑨𝒓𝒆𝒂
Small Area → HIGH Pressure
??
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10/21/2014
Barometers measure atmospheric pressure:
Pressure units summary:
1.000 atm
= 760.0 mmHg
= 760.0 torrs
= 101.3 kPa
= 101,300 Pa (N/m2)
= 14.7 psi (lbs./in2)
Pressure units summary:
1.000 atm
=
=
=
=
=
760.0 mmHg
760.0 torrs
101.3 kPa
101,300 Pa (N/m2)
14.7 psi (lbs./in2)
Why doesn’t the atmosphere crush us with all this
pressure?
Because we
push BACK
BALANCE: When
internal pressure
equals external
pressure
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10/21/2014
The Pressure of the Atmosphere:
The Pressure of the Atmosphere:
At sea level, the weight of the
atmosphere exerts a PRESSURE
equal to 14.7 pounds per
square inch (psi)
The Pressure of the Atmosphere…
… pushes air into our mouth and lungs when we
inhale.
…pushes liquid up a straw when we drink.
…pushes air and dirt into a vacuum.
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10/21/2014
How long could a straw be and still function?
Boyle’s Law:
At constant temperature: pressure and
volume are inversely proportional
As the volume goes down,
the pressure goes up.
As the volume gets larger,
the pressure gets smaller.
Water bottles & Ears
Popping on Airplanes:
Scuba Diving:
Applications of Boyle’s Law:
As the volume goes down, the
pressure goes up.
As the volume gets larger, the
pressure gets smaller.
Lungs, Pumps and Vacuum Cleaners:
Deep Sea Fishing:
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10/21/2014
Gay-Lussac Law:
At constant volume: temperature and
pressure are directly proportional
As the temperature goes up, the pressure goes up.
As the temperature goes down, the pressure goes down.
Gay-Lussac Law:
As the temperature goes up, the pressure goes up.
Charles Law:
At constant pressure: temperature and
volume are directly proportional
As the temperature goes up, the volume gets larger.
As the temperature goes down, the volume goes down.
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10/21/2014
Charles Law:
As the temperature goes down, the
volume goes down AND THE DENSITY
GOES UP.
As the temperature goes up, the
volume gets larger, AND THE DENSITY
GOES DOWN.
As the temperature goes down, the volume goes down.
As the temperature goes up, the volume gets larger.
Wind & Gas Laws:
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10/21/2014
Combine Gas Law:
• When the total quantity of gas is constant, we can
combine the three gas laws just described into one
relationship
𝑷𝟏 𝑽 𝟏
𝑻𝟏
= Constant
𝑷𝟏 𝑽 𝟏
𝑻𝟏
=
𝑷𝟐 𝑽 𝟐
𝑻𝟐
𝑷𝟏 𝑽 𝟏
𝑻𝟏
=
𝑷𝟐 𝑽 𝟐
𝑻𝟐
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