Introduction to Gases & Atmospheric Chemistry
GASES – ALL AROUND US….
- found all around us (literally) and very important to our daily lives
-e.g. breathing, heating, medical uses, scuba diving, air bags
-other examples??
-Ivory Soap – have you ever wondered?
http://www.youtube.com/watch?v=z1hzatoE1tg
http://www.piminski.com/2008_Jutube.html
COMPARISON OF SOLIDS, LIQUIDS AND GASES
Solids – hold a definite shape
Definite volume
Particles are closely packed
Can’t be compressed
Very little movement of particles
Strong attractive forces exist between particles
Particles have low Ek (little motion, Ek is kinetic energy)
Liquids - indefinite shape (takes shape of container)
Definite volume
Particles easily move past each other
Slightly compressible
Fluid (liquids flow)
Weak attractive forces exist between particles
Particles have more Ek (significant motion)
Gases - indefinite shape (takes shape of container)
Indefinite volume (particles spread out to fill container)
Particles have large spaces between them
Most of the volume of a gas is empty space
Particles rarely touch each other
Easily compressible
Fluid (gases flow)
Weakest attractive forces exist between particles
Particles have high Ek (constant motion)
KINETIC MOLECULAR THEORY
The properties and behavior of gases can be explained by the
these five main points –
1. All matter is composed of tiny particles
2. The particles are in constant motion (  temperature,  EK)
3. Forces of attraction and repulsion exist between the particles
4. Very large spaces exist between gas particles
5. Force of attraction between particles is very small
6. Particles have elastic collisions (energy is neither gained nor lost)
GAS PROPERTIES – VOLUME, V
Volume – amount of space that a gas occupies
measured in mL or L (or cm3)
1000 mL = 1.0 L
1 mole of any gas
occupies 22.4 L at STP
GAS PROPERTIES – TEMPERATURE, T
The Celsius scale is determined based on water freezing at
0C and boiling at 100C. This is quite arbitrary.
The Kelvin scale, however, is an absolute scale
Comparing the two scales
Kelvin = Degrees Celsius +273.15
Degrees Celsius = Kelvin -273.15
Convert the following:
150C =
1250C=
K
K
290K=
400K=
C
C
ABSOLUTE ZERO
This is believed to be the lowest temperature
possible for a gas to achieve and is often called
Absolute Zero. Hypothetically, all molecular
motion stops at this temperature.
Absolute Zero = -273.15C
GAS PROPERTIES – PRESSURE, P
Force - a push or a pull
Pressure - force per unit area
Pressure =
F
A
example:
Step on foot with running shoes
Step on foot with high heels
Force is the same, but the pressure is
different
Pressure results from the collision of gas particles with
the walls of the container in which the gas is
contained
SI units - Pascal, Pa
(derived unit - a combination of other units)
Other units – atm, mm Hg, psi, torr
Gas pressure depends on:
1. Area:
Increase Area, Decrease Pressure
Decrease Area, Increase Pressure
Area is Inversely related to Pressure
MEASURING PRESSURE
- Allow gas to exert a pressure on something that exerts a
pressure back
ie. Usually a column of Hg
Barometer - any device used to measure Earth’s atmospheric
pressure
Force holds Hg in column or it would run out
Earth’s atmosphere pushes on pool and supports column
When two forces balance, level of Hg becomes constant
 atm. pressure, Hg falls
 atm. pressure, Hg rises
PRESSURE CONVERSIONS
At sea level, 1 atm = 101.325 kPa
= 760 mmHg
= 760 torr
= 29.92 in. Hg
= 14.7 p.s.i
Convert the following:
a) 3.25 x 105 Pa =
b) 97.8 kPa =
c) 675 mmHg =
d) 300 kPa =
e) 798 mmHg =
f) 13.2 psi =
g) 16.4 psi =
h) 1.39 x 103 kPa =
i) 670 Pa =
kPa
psi
atm
mmHg
atm
kPa
mmHg
atm
kPa
GAS PROPERTIES – NUMBER OF MOLES, N
Number of moles = n
One mole represents 6.02 x 1023
particles
Why would one mole of any gas have
the same volume at STP?
STP – STANDARD TEMPERATURE & PRESSURE
As a reminder, STP is
OC and 101.3 kPa
What would STP be in K and atm?
SUMMARY - UNITS AND CONVERSIONS
Volume: V - L or mL
Temperature: T - °C or K
Kelvin= Celsius + 273.15
amount of gas measured in moles: n
Pressure: P - Pa or kPa, atm, mm Hg,
torr
STP- 101.325 kPa and 0 °C
INTRO TO THE GAS LAWS -
Phet lab
https://phet.colorado.edu/en/simulation/gas-properties
Computer lab day
BOYLE’S LAW
Discovered by Robert
Boyle in 1662
pressure is inversely proportional to volume
mathematical formula- P1V1=P2V2
A real life application is a syringe.
As volume increases, molecules must travel farther
to impact into the walls of the container, as such
the pressure is decreased.
BOYLE’S LAW EXAMPLE
50 mL of oxygen is at atmospheric pressure.
What is the pressure when there is a volume
is compressed to 35 mL?
V1= 50 mL
V1P1 = V2P2
P1 = 101 kPa
P2 = V1P1/V2
V2 = 35 mL
P2 = (50mL)(101kPa)/35 mL
P2 = ?
P2 = 144.3 kPa
BOYLE’S LAW DEMONSTRATION
Example: syringe
As the water is drawn up into the syringe,
the volume of the air inside is decreased.
The air molecules have less space to travel,
and therefore, collide into the walls of the
container more often. The pressure
increases because there are more molecule
impacts per unit time. This pressure holds
the water in the syringe.
CHARLES’ LAW
Discovered by Jacques Charles in 1787
volume is proportional to temperature
mathematical formula: V1 = V2
T1 T2
An example would be a hot air balloon rising and
falling. Hot air is pushed into the balloon. The air
expands and fills the balloon. To come down, air
from the balloon is released.
CHARLES’ LAW EXAMPLE
A gas occupies 100 mL at 20 °C . At what
temperature will it occupy 200 mL?
V1= 100mL
V1/T1 = V2/T2
T1= 20 °C = 293K
T2= V2T1/V1
V2= 200 mL
T2= (200mL)(293K)/(100mL)
T2= ?
T2= 586 K
CHARLES’ LAW DEMONSTRATION
Example: Hot Water Balloon
When the water bottle is dispersed into the
hot water, the air molecules begin to
expand, rise and move faster.
So, the molecules are pushed up from the
bottle and inflate the balloon.
PRESSURE- TEMPERATURE LAW
Also called the
Gay-Lussac law
Pressure is proportional to temperature
mathematical formula: P1 = P2
T1
T2
An example would be how bike tires lose pressure
during the winter. As air cools, it contracts. So a
bike tire will be flat after the winter months
because the air inside has decreased in
temperature.
PRESSURE- TEMPERATURE LAW EXAMPLE
Temperature is increased from 40 K to 200 K. If the
final pressure was 80 kPa, what was the initial
pressure?
T1 = 40 K
P1/T1 = P2/T2
P1 = ?
P1 = P2T1/T2
T2 = 200 K
P1 = (80kPa)(40K)/200K
P2 = 80 kPa
P1 = 16 kPa
PRESSURE- TEMPERATURE LAW
DEMONSTRATION
Example: beads in a bottle
The beads represent air molecules in a container.
There are the same number of beads in each,
however, the second bottle has a higher
temperature.
The bottles are shaken to represent the movement
of the molecules. At higher temperatures,
molecules move faster and therefore, impact the
container walls more often. This demonstrates the
increase in pressure.
REVIEW
Boyle’s Charles’ P-T law
law
law
variables P and V V and T P and T
constant
T and n
P and n
V and n
formula
P1V1=P2V2
V1 = V2
T1 T2
P1 = P2
T1 T2
Other
information
atmospheric Always do
Also called
pressure =
calculations Gay101 kPa
in Kelvin
Lussac’s
law
COMMON MISTAKES
Confusing the laws
temperature problems can only be solved using
the Kelvin scale
difference between SATP and STP
SATP- 100 kPa and 25 °C
STP- 101.325 kPa and 0 °C
ANY QUESTIONS ?