Transcript Gas Laws
Gas Laws
Molecules In The Air
How do we know there are molecules
in the air?
Has anyone ever had wind burn?
How about smelled a hamburger when
you drove by McDonalds?
These examples demonstrate that air
is made up of constantly moving
molecules.
Kinetic Molecular Theory
Kinetic energy is perfectly maintained in
“elastic” molecular collisions.
Molecules are in constant Motion.
– Vibrational motion.
– Translational motion.
Tiny particles called “molecules” make up all
matter.
Kinetic Molecular Theory
Describes only “Ideal Gases”
– Ideal gases follow the gas laws in all
conditions of pressure and temperature.
Ideal gases assume particles of gas
have no volume or intermolecular
attraction.
Ideal gases have perfectly elastic
molecular collisions.
In REALITY!
Real gases have
volume.
Real gases have some
intermolecular
attraction.
Real gases can be
liquefied and solidified
by cooling and applying
pressure.
In reality,
experimentation shows
us that real gases do
not follow “Ideal
Behavior”
Gases Are All Around Us!
Many gases are invisible, but some we
can see.
Iodine Vapor is Pink.
Chlorine Gas is Yellow-Green.
Smoke, clouds, and fog are NOT
gases!!
Gases Are All Around Us!
Some gases we can
smell.
Hydrogen Sulfide
smells like rotten eggs.
In natural gas, a smell
has been added for
our protection.
Other gases we can’t
smell at all.
Gases Are All Around Us!
Gases have mass.
Balloons that are
filled with air
weigh more than
those that are unfilled.
When air moves it
can do work. For
example tornadoes
or windmills.
Gases Are All Around Us!
Gases occupy
space, or have
volume.
Examples:
– Inflated Balloon
– Our Lungs
– Scuba Tanks
Gas Behaviors
Compressibility
– The volume of a gas can be decreased by
increasing the pressure.
Permeability
– The mixing of molecules in a container.
Diffusion
– The ability to spread from a high concentration
to a lower concentration.
Expansibility
– The ability of a gas to expand and fill a
container of any size.
Under Pressure
What causes pressure?
Pressure is caused by the collision of
gas molecules.
The molecules can collide with each
other or with the walls of their
container.
Atmospheric Pressure
Air exerts pressure on earth.
– Gravity holds air molecules in the earth’s
atmosphere.
Atmospheric Pressure occurs when
those air molecules collide with each
other or other objects.
Atmospheric pressure decreases as
you move to a higher elevation.
Gas Laws
There are several
different gas law
equations.
Variables:
–
–
–
–
–
–
–
V
P
T
n
R
d
Variables
V= volume in liters.
T= temp in Kelvins.
P= pressure in atm,
mmHg, or kPa.
n= number of moles
of gas.
R= the universal
gas constant.
d= gas density in
g/L.
= molar mass of a
gas in g/mol.
Units of Pressure
Pressure is defined as a force over a
specific area.
– P=F/A
English system:
– lbs/in2 = PSI
Metric system:
– N/M2=Pascal
Boyle’s Law
Robert Boyle
(1627-1691)
At a constant
temperature,
volume and
pressure of a gas
are inversely
proportional.
Boyle’s Law
As pressure increases, volume
decreases, and vice versa.
V1P1=V2P2
V œ 1/P
Remember the volume of a gas can
NOT be squeezed down to zero!
Charles’s Law
Jacques Charles
(1746-1823)
At constant
pressure, the
volume of a gas and
temperature are
directly
proportional.
Charles’s Law
As temperature increases, volume
increase, and vice versa.
V1/T1=V2/T2
VœT
Gases expand as they get warm , and
contract as they cool.
Gay-Lussac’s Law
Joseph Gay-Lussac
(1778-1850)
At constant
volume, gas
temperature and
pressure are
directly
proportional.
Gay-Lussac’s Law
As temperature increases, pressure
increases, and vice versa.
P1/T1=P2/T2
TœP
This is why aerosol cans say “Do not
incinerate!”
Combined Gas
To simplify life, Boyle’s Law, Charles’s
Law and Gay-Lussac’s Law have been
put together into one mathematical
expression.
Combined Gas Law
V1P1 = V2 P2
T1
T2