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Gases

Gases. Objectives: 1. State the kinetic theory of matter. 2. Use the kinetic theory to explain states of matter. Review/Preview. What is kinetic energy? Kinetic Molecular Theory applies to gases. What would “kinetic-molecular” theory logically discuss?. The Kinetic-Molecular Theory.

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Gases

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  1. Gases Objectives: 1. State the kinetic theory of matter. 2. Use the kinetic theory to explain states of matter

  2. Review/Preview • What is kinetic energy? • Kinetic Molecular Theory applies to gases. What would “kinetic-molecular” theory logically discuss?

  3. The Kinetic-Molecular Theory • Def.: describes the behavior of gases in terms of particles in motion • Kinetic-molecular theory makes several assumptions about the size, motion, and energy of gas particles.

  4. Kinetic-Molecular Theory Basic Assumptions : • Size: Gases are made of small particles separated by A LOT of empty space. • This means the volume of the particles is negligible; assume volume = 0. • Because particles are so far apart, there is no significant attractive or repulsive force between them.

  5. Kinetic-Molecular Theory Basic Assumptions : • Motion: Particles are in constant, random motion, moving in a straight line until they collide with something. • They can collide with the container walls or with each other. • Collisions with each other are considered to be elastic collisions: a collision in which no kinetic energy is lost (but it may be transferred).

  6. Kinetic-Molecular Theory Basic Assumptions : • Energy: Kinetic energy is determined by a particle’s mass and velocity (KE = ½ mv2) • Since temperature is a measure of the average kinetic energy of the particles in a sample of matter, then temperature is directly proportional to average kinetic energy of a gas sample. • What happens to temperature if particles in a sample slow down? • Why?

  7. Review • Complete Workbook (p.73): 1-4 together as a class.

  8. Explaining the Behavior of Gases • Low density (What is density?)– lots of empty space between particles • Compression and expansion - stress ball demo

  9. Explaining the Behavior of Gases, continued…….. • Diffusion and effusion • What is diffusion? • Def: the movement of one material through another (examples: perfume, blood gases) • Particles move from areas of high concentration to areas of low concentration • Lighter (less mass) particles diffuse more rapidly

  10. Explaining the Behavior of Gases, continued…….. • Diffusion and effusion, continued…. • Effusion: when a gas escapes through a tiny opening (think punctured tire) • Inverse (??) relationship between effusion rates and molar mass • So which gas would effuse (escape) faster, ammonia (NH3) or hydrogen chloride (HCl)?

  11. Gas Pressure • Pressure: force per unit area (psi or N/m2) • When gas particles collide with a container wall, they exert force, creating pressure. • Air pressure = column of air pushing down on the ground. • Why is air pressure lower at the top of a mountain than it is at sea level? • SI unit for pressure: pascal (Pa) = 1 N/m2 • Others: 1 atm = 760 mm Hg = 760 torr = 101.3 kPa

  12. Assignment • Workbook (p.73): 5-12 together • Problem-Solving Lab (p.390)

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