Friday, Jan. 10th: “A” Day
Monday, Jan. 13th: “B” Day
Agenda
Begin Chapter 12: “Gases”
12.1: “Characteristics of Gases”
Pressure, newton, pascal, STP, kinetic-molecular theory
Pressure Demos
In-Class/Homework:
Pg. 422: #1-12
Concept Review: “Characteristics of Gases”
Quiz over this section next time!
Gases
Chapter #12
Gases are Unique
Gases have unique properties because the
distance between the particles is much
greater than in a liquid or a solid.
Properties of Gases
1. Gases are Fluids
– Gases are considered fluids because they have the
ability to FLOW.
2. Gases Have Low Density
– Because of the large distances between gas
molecules, most of the volume occupied by a gas is
empty space.
3. Gases are Highly Compressible
– Applying a small pressure will move the gas
particles closer together and will decrease the
volume.
4. Gases Completely Fill a Container
– A gas expands to fill the entire volume available.
Pressure Demos
Plastic Bag in Beaker
Straw Through Potato
The Can Crusher
Egg in a Bottle
Vacuum Pack People
(we’ll wait until the end to do this one!)
Air pressure is caused by collisions of
gas molecules.
Measuring Pressure
Pressure: the amount of force exerted per unit
area of surface (force/area)
Newton (N): the SI unit of force
The force that gives an acceleration of 1 m/s2
to an object whose mass is 1 kg.
1 N = 1 kg∙1 m/s2
Pascal (Pa): the SI unit of pressure
The force of 1 N exerted over an area of 1 m2
1 Pa = 1 N/m2
A Mercury Barometer Measures
Atmospheric Pressure
Atmospheric Pressure
 At sea level, the atmosphere keeps the
mercury (Hg) in a barometer at 760 mm,
which is 1 atmosphere.
 1 mm of Hg is also called a torr, named after
Italian physicist Evangelista Torricelli,
who invented the barometer.
(Handsome devil, isn’t he?)
Equivalent Pressure Units
In this chart, your book uses spaces instead of
commas…
Standard Temperature & Pressure
(STP)
To study the effects of changing temperature
and pressure on gases, scientists have
specified a set of standard conditions called
standard temperature and pressure, or STP.
STP = O˚C and 1 atm
Sample Problem A, Pg. 420
Converting Pressure Units
Convert the pressure of 1.000 atm to
millimeters of mercury.
1.000 atm X 101,325 Pa = 101,325 Pa
1 atm
101,325 Pa X 1 mm Hg =
133.322 Pa
760.0 mm Hg
(4 sig figs)
Additional Practice
The vapor pressure of water at 50.00˚C is
12.33 kPa. What is this value in millimeters of
mercury?
12.33 kPa X 1,000 Pa = 12,330 Pa
1 kPa
12,330 Pa X 1 mm Hg =
133.322 Pa
92.48 mm Hg
(4 sig figs)
The Kinetic-Molecular Theory
Kinetic-molecular theory: a theory that
explains that the behavior of physical systems
depends on the combined actions of the
molecules constituting the system.
In Plain English: the kinetic-molecular theory
is a model that is used to predict gas behavior.
The Kinetic-Molecular Theory
1. Gas particles are in constant rapid, random
motion.
2. Gas particles are very far apart relative to
their size.
3. The pressure exerted by a gas is a result of
the collisions of the molecules against the
walls of the container.
4. The collisions are considered elastic (energy
is completely transferred during collisions).
Gas Temperature is Proportional
to Average Kinetic Energy
Gas Temperature is Proportional to
Average Kinetic Energy
For a 10˚C rise in temperature from STP, the
average energy increases about 3%, while the
number of very high-energy molecules about
doubles or triples.
In-Class/Homework
Section 12.1 review: Pg. 422, #1-12
Concept Review: “Characteristics of Gases”
Be ready for a quiz next time
over this section!