Gases Objectives 1 State the kinetic theory of

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 § 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.

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.

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).

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?

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

Explaining the Behavior of Gases 1. Low density (What is density? ) – lots of empty space between particles 2. Compression and expansion - stress ball demo

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

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)?

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 k. Pa

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