Standard 4
Gases and Their
Properties
Chapters 2, 13, and 14
Santa Fe High School
Mr. O’Brien
The Temperature
Scale (std.4e)
How is temperature and movement related?


Decreases particles slow down
Increases particles move faster
What are some Units of Temperature?


Kelvin (K)
 SI unit (accepted scientific unit)
 Preferred unit because coldest temp is 0K.
Celsius (oC)
 Same degree value as Kelvin but the
coldest temperature possible is -273oC.
Checking for Understanding
Why is the Kelvin scale more accurate description
of temperature than the Celsius scale?
Since temp measures kinetic energy it only makes sense that scale
starts at zero. Compared to negative values for others.
Is their a limit to how LOW temperature can
measure?
YES. ZERO KELVIN. There is nothing slower than molecules that
have stopped.
Key Term
Temperature
Measurement of Kinetic Energy
(movement of particles)
The Temperature Scale
Checking for Understanding
(std.4e)
How to convert between temperature scales?
 oC

Extra HONORS Information
Fahrenheit scale



+ 273.15 = K
1st temp. scale
Based on known lowest & highest
temp. points in Western Europe:
Converting between temperatures:
 oF
= (1.8 x oC) + 32
25oC⇨ ? Kelvin
25 + 273.15 = 298.15 K
-5oC⇨ ? Kelvin
(-5) + 273.15 = 268.15 K
301K ⇨ ? Celsius
27.85oC = 301 K - 273.15
0K ⇨ ? Celsius
-273.15oC = 0 K -273.15
Extra HONORS Information
 Conversion Practice:


100oF → oC = 37.4 oC
25oC → oF
= 77 oF
Checking for Understanding
Absolute Zero
Is 0oC as cold as 0K? Explain or
cite specific evidence.
(std.4f)
What is absolute zero?

temperature at which all motion of molecules
stop (0 K)

THERE IS NO TEMPERATURE LOWER
THAN ABSOLUTE ZERO!
Absolute Zero Still a Theory
The closest scientist have ever reached is
0.000 000 000 001K
3rd
law of thermodynamics says everything must have
some energy.
(figure 1) Lowest temp. 1x10-12 K
achieved Sept. 2003 at MIT Univ.
Kinetic Molecular Theory
& Pressure (std.4a)

What is the “Kinetic Molecular Theory”?
“Idea of how Molecules Move”
1.
2.
3.
Gases are small particles that are
separated by empty space.
Particles move RANDOMLY!!
Molecules have no attraction for each
other
•
4.
no intermolecular forces holding them!!!
Particles move in a straight line until they
collide with other particles or boundaries.
•
5.
(figure 1) Shows space between gas particles
and the random motion of them.
ELASTIC collisions!!!!
Gas particles move at high speeds (near
speed of sound).
(figure 2) In solid states, intermolecular forces
are strong. In the gas state, no intermolecular
forces exist. Thus no attraction between gas
particles.
(figure 3 ) Shows how elastic collisions work.
761 mi/hr
Key Term
Kinetic Molecular
Theory & Pressure
Pressure
Force applied to a wall of a
container by particles
(std.4a)
Why are Gases and Liquids considered FLUIDS?

molecules that freely move past each other in random directions.
How is pressure created?


Pressure is created when gas particles collide with the walls of its
container.
More collisions against the walls = more pressure
Checking for Understanding
Using your knowledge of
1. how gas moves
2. how pressure is created
explain how does a balloon holds it’s shape?
Checking for Understanding
Using your knowledge of
how pressure is created
Compare pressure at different altitudes.
Key Term
Diffusion (std.4b)
Diffusion
Movement of one material
through another
How do gas particles “Diffuse”? Do different gas particles diffuse
at different rates (speeds)?
 Particles diffuse from an area of
high concentration to a low
concentration.

Heavier molecules diffuse slower.
HCl
NH3
Checking for Understanding
Checking for Understanding
What property of gas behavior accounts for
the fact that gas particles seem to be
equally distributed throughout a sample.
A student opens two vials with the following
chemicals:
H2 and O2
Which will diffuse faster through the room?
Key Term
Standard
Temperature &
Pressure (std.4d)
Barometer
Instrument used to measure
atmospheric pressure
What is STP?
How does a Barometer work?




Air pressure pushes down on liquid Mercury
in a pool causing it to rise in the tube.
The height of the tube is listed in millimeters
and reflects air pressure.
At sea level the air pressure is

Standard Temperature & Pressure
273K (0oC) and 1 atm
Why do we use STP?

We observe and record gas
measurements at these conditions.
1atm (atmospheres) = 760 mm Hg
Checking for Understanding
2atm ⇨ ?mm Hg
1520 mm Hg
380 mm Hg ⇨ ?atm
0.5 atm
1.5atm ⇨ ?mm Hg1140mm Hg
570mm Hg ⇨ ?atm
0.75 atm
Gas Laws
What factors are expressed in the
COMBINED GAS LAW?
(std.4c)
P1 V1 = P2 V 2
T1
T2
What are 4 factors that influence gas
behavior?




Pressure
Volume
Temperature
Amount of gas
Checking for Understanding
What factor remains constant (unchanged) in the
combined gas law?
What temperature unit should only be used in the
Combined Gas Law?
A weather balloon has a volume of 145 L at seal
level where the temperature is 17oC and the
pressure is 1.0 atm. The balloon rises to a point
in the atmosphere where the temperature is 73oC and the pressure has decreased to 0.5 atm.
What is the new volume of the balloon?
What do the subscripts mean?
P1 = initial value

P2= final value
Factors must have same
values.
Gas Laws (std.4c)
What factors does Boyle’s Law account for?

↑ Pressure  ↓Volume

↓ Pressure  ↑ Volume

INDIRECT relationship
P1V1 = P2V2
T1
T2
Checking for Understanding
The pressure of a sample of helium in a 1.00Lcontainer is 0.5atm. What is the new pressure if
the sample is placed in a 2.00L container?
0.25atm
The pressure of a 2L balloon is 380mm Hg.
What is the new volume if the pressure is
increased to 760mm Hg?
1L
(figure 1) Boyle’s law explained in a graph. As
pressure decreases, volume increases.
Gas Laws (std.4c)
What factors does Charles Law account for?

↑ Volume ↑ Temperature

↓ Volume ↓ Temperature

DIRECT relationship
P1V1 = P2V2
T1
T2
(figure 1) Charles’s Law equation.
Temp. must be expressed in Kelvin.
Checking for Understanding
A gas at 373K occupies a volume of 1.00L. At what
temperature will the volume increase to 2L? Remember that Temp.
746K
must be in Kelivn!
A gas syringe contains 40mL of gas at 127oC. Determine the
temperature of the gas in Kelvin if the volume is increased to
50mL.
500K
(figure 2) Charles's law explained in a graph. As
temp. decreases volume decreases.
Gas Laws (std.4c)
What factors does Gay Lussac’s Law account for?

↑ Pressure ↑ Temperature
P1V1 =

↓ Pressure ↓ Temperature

DIRECT relationship
T1
P2V2
T2
Checking for Understanding
The pressure in an automobile tire is 1200
mm Hg at 127oC. What will be the pressure
if the temperature warms up to 227oC?
1500 mm Hg
Remember that Temp.
must be in Kelivn!
A container at STP is heated to 546K. What
will be the new pressure?
Remember at STP
1atm (760mm Hg)
&
273K
2atm
or
1520 mm Hg
(figure 2) Notice as temp. drops, gas
particles move slower and pressure
decreases. As heat is added, particles
speed up and pressure increases.
(figure 3) Gay-Lussac’s graph.
Gas Laws
(Honors)

Dalton’s Law of Partial Pressures:



Total pressure of a mixture of gases
is equal to the sum of the pressures
of all the gases in the mixture.
Ptotal = P1 + P2 + P3…
Let’s try: Find the total pressure for
a mixture that contains four gases
with partial pressures of 5.00kPa,
4.56kPa, 3.02kPa, and 1.20kPa.


Ptotal = 5.00 + 4.56 + 3.02 + 1.20
Ptotal = 13.78 kPa
(figure 1) When cylinder “a” and “b” combine
their pressures also combine.
(figure 2) Composition of air
at sea level. Note 101.3kPa =
1 atm.
Ideal Gas Law
(Honors)


The previous gas laws explains
relationships for “fixed amounts.”
But ideal gas accounts for the
changing the number of gas particles
present.
(figure 1) Figure to the right




shows relationship of Ideal
gas law with other gas laws.
Any change will affect the other
variables (P,V,and T)
Can be rearranged to find any variable
R: ideal gas constant
n: # of moles of a gas
If using units
these units:
R constant
L*atm
0.0821
mol*K
PV = nRT
(figure 3) Ideal Gas Law
equation. Temp. must be
expressed in Kelvin if using the
“R” constants presented.
(figure 2) The table to he right
shows “R” constants
associated with different
pressure units.
L*kPa
8.314
mol*K
L*mm Hg
mol*K
62.4
Ideal Gas Law
(Honors) (cont.)

How many moles of hydrogen
gas occupy a volume of 11.2L
at STP?


Remember that 1mol = 22.4L
What is the temperature of
0.25mol of chlorine gas at 655
torr if the volume is 3.5L?
PV = T
nR
146.9 K
(655torr)(3.5L)
(0.25)(62.4)
= T
=
T
11.2L 1 mol = 0.5mol
22.4L