•Monoatomic Gas: Made of one atom, like He
•Diatomic Gas: Made of two atoms, like Cl2 or H2
*This is the case for Br, I, N, Cl, H, O, F
Also known as Miss BrINClHOF (Brinklehoff)
•Polyatomic Gas: Made up of more than two atoms, like
CO2, NO2, or CH4 (methane)






Gases have mass
It is easy to compress a gas
Gases fill their containers
completely
Gases diffuse through each
other easily
Gases exert pressure on
their surroundings
The pressure of a gas
depends on its temperature


Gases are composed
of a large number of
particles that behave
like hard, spherical
objects in a state of
constant, random
motion.
Basically, gas
particles are like
billiard balls in a 3-D
pool table, and they
are all moving all
over the place all the
time in different
directions



These particles move in a straight line until
they collide with another particle or the
walls of the container.
Then they bounce off, and move again: these
collisions are elastic
Gas Molecule Motion


There is no force of
attraction between gas
particles or between
the particles and the
walls of the container.
Keep in mind that
things aren’t repelled,
either….no attraction,
no repulsion…



Collisions between gas particles or
collisions with the walls of the
container are perfectly elastic.
None of the energy of a gas
particle is lost when it collides
with another particle or with the
walls of the container.
This is why gases take the shape
of their container!
The energy of the system is
constant as long as the pressure
and temperature remain constant.


The average kinetic energy of a
collection of gas particles depends
on the temperature of the gas and
nothing else.
Think back to the fact that temperature is
a measure of Kinetic Energy (the random
motion of molecules)



These particles are much smaller than the
distance between particles. Most of the
volume of a gas is therefore empty space.
Compared to the container, the volume of the
gas is zero. So, we say the volume of the
container is the volume of the gas
The volume of the gas in an empty soda bottle
is?
1.
2.
3.
4.
5.
6.
Gases consist of very small particles , each of which
has a mass.
The distance separating gas particles is very large
so much so that we say the volume of the gas is
negligible as compared to the volume of the
container (the gas itself has no volume)
Gases exert no force on one another
Gas particles are in random, rapid, constant motion
Collisions with other gas particles or the walls of
the container are elastic (no energy lost)
The average KE of a gas depends on the
temperature of the gas
We measure gases in several ways…




Volume
Temperature
Pressure
Number of Moles
=V
=T
=P
=n

Temperature is a measure of heat; more specifically it
is the (average) measure of the random kinetic energy
of the molecules in an object

Kinetic energy: Energy of motion

More motion = More KE = Higher temperatures

Less Motion= Lower KE = Lower temperatures


For most scientists, the Celsius scale is used
However, we need to use the Kelvin scale for
gas laws


Why this strange and bizarre scale that uses a boiling
point of 373K and a freezing point of 273K for
water?
Well, it’s because our “normal” temperature scales
are based upon numbers that make sense to use (or
not)

(like freezing at 0°C and boiling at 100 °C) or are a bit
more convoluted (like the Fahrenheit scale, where zero
comes from the temperature of ice, water and NH4Cl and
body temperature was 98 °F and still water with ice was 32
°F. )


The Kelvin scale bases temperature on an
absolute scale, where temperatures correspond
to the amount of motion of the particles
Absolute zero (O K) is when there is no
molecular motion (at all)


Scientists have gotten close to zero K, but not quite
there.
It exists naturally in deep space



Calculations using temperature of zero could
be undefined or have no value (which really
can’t be)
Can’t have negative volumes in our equations,
because that is impossible (from using negative
temperatures values in the variables)
The Kelvin scale avoids all of these issues



Is based in Absolute Zero, which is -273°C
0K= -273°C
273K=0°C
To convert between K and °C,
°C + 273 =K
or K -273 = °C
It’s that simple, which is good since no gas laws
calculations can use °C

We usually measure volume in Liters (L), but
sometimes in other metric units
1L = 1000mL
1L = .001m3
We will use these conversions- be sure to know
them!


Gas pressure is created by the molecules of gas
hitting the walls of the container. This concept
is very important in helping you to understand
gas behavior. Keep it solidly in mind. This idea
of gas molecules hitting the wall will be used
often.
Pressure is force measured over an area
P=Force/ area
and yes, Physics children,
Force = mass (acceleration)





atmospheres (atm)
millimeters of mercury (mm Hg)
Pascals (= Pa)
kiloPascals (= kPa)
Standard pressure is defined as:
1 atm
1atm =760.0 mm Hg
1 atm=101.325 kPa

Manometers- Measure the pressure of a gas as
compared to the outside world




We’ve been here before. Calm down about it.
Remember that 1 mole is 6.02E23 pieces of
something- in this case, usually molecules of gas
(but sometimes atoms, if not a diatomic gas).
Also, 1 mol gas at STP (Standard Temp/Pressure)
= 22.4L
“= “means occupies, takes up, etc

Relates
pressure and
volume, while
temperature and
number of moles
are constant (so
they do not
appear in the
equation)
P1V1=P2V2



In a closed rigid container of a gas at a constant
temperature, the pressure times the volume
remains constant (P1V1=k)
Pressure and volume are inversely related
The P1 is the pressure at the first volume (V1),
while P2 is the pressure at the second volume (V 2).

The product of
pressure and
volume remains
constant as long as
the temperature
remains constant.
(The number of moles
must also remain
constant.)
Volume
Pressure
• When volume is
high, pressure is low
• When the volume is
low, pressure is high




If a balloon with a volume of 3L is under a
pressure of 1 atmosphere, determine the new
volume if the pressure is changed to .8 atm.
We are given P1, V1, and P2. We are asked to
find V2
Two key words here are new and changed- to
ID these measurements as linked (having the
same subscript)
What is the new volume?

Charles’ law relates
volume and
temperature, at a
constant pressure
and number of
moles in a flexible
container. Since the
pressure and
number of moles
are constant, they
do not appear in the
equation.
V1/T1=V2/T2


In a closed container of a gas at a
constant temperature, the pressure
times the volume remains constant
(P1V1=k)
The P1 is the pressure at the first
volume (V1), while P2 is the pressure at
the second volume (V 2).



V1/T1=V2/T2 can be rearranged to read
V1T2=V2T1
Why would we care to rearrange this? This
means no division in the equation. You can
use it either way, just remember that they are
DIRECTLY PROPORTIONAL.



As the temperature increases, the volume
increases.
As the temperature decreases, the
volume decreases.
Temperature and volume are
proportionally related.



Think again about temperature- it is the
KE of the gas particles.
Think about what the volume is a result
of: the force that the gas molecules are
exerting of the container
Think about how if something hits
another thing at a higher speed- it hits
with more force. More force is pushing
harder. Pushing harder means further.
This means greater volume when we are
dealing with a flexible container!


Relates pressure and temperature, when
volume is kept constant (P1/T1=k)
P1/T1= P2/T2
Or

P1T2=P2T1



(P1V1)/ T1=(P2V2)/T2
Takes all other gas laws into account, even if
you can’t see them here (they cross out of the
equation)
When in doubt about most of the guy’s laws,
you can use this one, because when the
pressure, volume, or temperature is constant,
you have the law you need.