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Friday, Jan. 10 th : “A” Day Monday, Jan. 13 th : “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” - PowerPoint PPT Presentation
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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!