# Chapter 12 – Gas Laws by shuifanglj

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```									Chapter 13 –

Gas Laws
Properties of Gases
Kinetic Molecular Theory
• Explains behavior of gases at
molecular level
• Developed in the Mid-1800’s
• Assumes an ideal gas
– NO interactions between gas particles
– Especially in collisions.
Collisions
• Assume collisions are elastic in ideal gas

– Elastic – no energy transferred
– Inelastic – energy transferred from one
particle to the other, usually in the form of
heat

• no net attractive or repulsive forces in gas
particles collisions
Real Gases
• Must consider transfer of energy in
collisions due to attractions and
repulsions of molecules.
• Must consider the volume of gases
Gases are Fluids
• WHAT!?!?!
• Yes; a fluid is “a substance that
flows”.
– Liquid examples include syrup, Hg, Br2
• Gases flow like liquids
– Dry Ice
door. What happens?
Density
• Solids have the highest densities
– atoms are tightly packed together.
• Liquids have high densities
– free to move past one another
– still very close to each other.
• Gases have very low densities.
– Atoms are far apart
– Gas volumes are mostly empty space
– Ignore volume of gas particles and use volume
of container as volume of gas.
Gases are compressible
• Gases can be compressed up to 100x
the original volume.
• For example, 30 mL of air can
compress to 0.30 mL.
• Why can’t I do it in the syringe?
Average Temperature
• Temperature is AVERAGE kinetic
energy where KE=1/2 mv2
• Molecules may possess any value of
kinetic energy, from zero to infinity
Average Kinetic Energy
Pressure
• P = Force/Area = N/m2 = Pascal (Pa)

• Gas pressure is exerted on all walls
and in all directions of a container.

• Pressure is what keeps walls up and
is responsible for aerosol cans.
– Examples include pump sprays, oil
pumps, and vacuum cleaners
Atmospheric Pressure
• The pressure exerted by the particles in the
atmosphere that surrounds Earth is called
atmospheric pressure, or air pressure.
• Air pressure varies at different locations on
Earth.
Atmospheric Pressure
• The atmosphere always exerts a
pressure on Earth.
• Due to the mass of air above us and
the gravitational pull of the earth.
• Standard atmospheric pressure at
sea level is 14.7 psi (pounds per
square inch) or 1 atmosphere (atm)
Air Pressure
• Air pressure is
measured using a
barometer.

• A barometer consists
of a thin tube closed
on one end and filled
with mercury.
Gas Pressure

• The tube is placed
so that the level of
the mercury is
determined by air
pressure.
• The mercury rises
when the air
pressure increases
and falls when the
air pressure
decreases.
Gas Pressure – Mercury
barometer
THERE IS NO SUCH THING
AS SUCTION!!!
• Gases move from areas of high pressure to areas
of low pressure.
• That is why we have wind outside.
• Dyson’s vacuum cleaner claim to “Never Lose
Suction!”
• Vacuum cleaner works
– A motor removes air from inside the sweeper
– This creates a vacuum (hence “vacuum” cleaner).
– Air particles move to low pressure area to even things
out.
– As the air travels into the sweeper, it picks up particles
from the carpet and carries them with it.
• JUST THE SAME WAY THAT WIND CARRIES DIRT
AND OTHER THINGS WITH IT!!!
Pressure conversions
• 1.0 atm = 14.7 psi (pounds per square inch)
• 1.0 atm = 101,325 Pascals (Pa)
• 1.0 atm = 101.325 KiloPascals (kPa)
• 1.0 atm = 760 mmHg
• 1 mmHg = 1 torr

• YOU must know these conversions,
they will NOT be given to you!
Boyle’s Law
• Relates Volume and Pressure
• You will investigate this relationship
tomorrow.
• P1V1 = P2V2
Thank you!!!
• Your attention today is greatly
appreciated!

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