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 : 1.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 : 2.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 : 3.Energy: Kinetic energy is determined by a particle’s mass and velocity (KE = ½ mv 2 )  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 1.Low density (What is density?) – lots of empty space between particles 2.Compression and expansion - stress ball demo

9. Explaining the Behavior of Gases, continued…….. 3.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…….. 3.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 (NH 3 ) or hydrogen chloride (HCl)?

11. Gas Pressure  Pressure: force per unit area (psi or N/m 2 )  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/m 2  Others: 1 atm = 760 mm Hg = 760 torr = 101.3 kPa

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