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

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”

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

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  1. Friday, Jan. 10th: “A” DayMonday, Jan. 13th: “B” DayAgenda • 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!

  2. GasesChapter #12

  3. Gases are Unique • Gases have unique properties because the distance between the particles is much greater than in a liquid or a solid.

  4. Properties of Gases • Gases are Fluids • Gases are considered fluids because they have the ability to FLOW. • Gases Have Low Density • Because of the large distances between gas molecules, most of the volume occupied by a gas is empty space. • Gases are Highly Compressible • Applying a small pressure will move the gas particles closer together and will decrease the volume. • Gases Completely Fill a Container • A gas expands to fill the entire volume available.

  5. PRESSURE!

  6. 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!)

  7. Air pressure is caused by collisions of gas molecules.

  8. 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

  9. A Mercury Barometer Measures Atmospheric Pressure

  10. 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?)

  11. Equivalent Pressure Units • In this chart, your book uses spaces instead of commas…

  12. 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

  13. 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)

  14. 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)

  15. 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.

  16. The Kinetic-Molecular Theory • Gas particles are in constant rapid, random motion. • Gas particles are very far apart relative to their size. • The pressure exerted by a gas is a result of the collisions of the molecules against the walls of the container. • The collisions are considered elastic (energy is completely transferred during collisions).

  17. Gas Temperature is Proportional to Average Kinetic Energy

  18. 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.

  19. 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!

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