Friday, Jan. 10th: “A” DayMonday, Jan. 13th: “B” Day

AgendaBegin Chapter 12: “Gases”12.1: “Characteristics of Gases”

Pressure, newton, pascal, STP, kinetic-molecular theoryPressure DemosIn-Class/Homework:

Pg. 422: #1-12Concept Review: “Characteristics of Gases”

Quiz over this section next time!

GasesChapter #12

Gases are UniqueGases have unique properties because the

distance between the particles is much greater than in a liquid or a solid.

Properties of Gases1. 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 DemosPlastic Bag in BeakerStraw Through PotatoThe Can CrusherEgg in a BottleVacuum Pack People

(we’ll wait until the end to do this one!)

Air pressure is caused by collisions of gas molecules.

Measuring PressurePressure: 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/s∙ 2

Pascal (Pa): the SI unit of pressureThe 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. 420Converting 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 PracticeThe 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 TheoryKinetic-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 Theory1. 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, #1-12Concept Review: “Characteristics of Gases”

Be ready for a quiz next time over this section!