A Little Gas Problem Ideal Gas Behavior

Basic Kinetic Molecular Theory Basic states of matter: solid, liquid, gas, and plasma (not emphasized) Particles held together by intermolecular forces- essentially positive-negative attractions

Solids versus Liquids Closely-packed particles High density Definite shape Definite volume High structure/order Low molecular speed Many intermolecular connections More spacing between particles Definite volume No definite shape Less structure/order Higher molecular speed Some intermolecular bonds broken Solids: Liquids:

Click here for simulation What about the gases Wide-open spaces Very low density Shape of container Volume of container Randomness/chaos High molecular speed No molecular connections Gases or vapors Click here for simulation

Solids, liquids & Gases Gases: loose and free, fast and furious Liquids: layers, some structure and attachment Solids: structure, restricted motion, order

How does this all work? In solid form the molecules have low energy, many connections and little motion Energy added, more moving, connections broken Faster means spreading out and breaking connections

What gases are like… Particles are widely spread out They move freely and independently Many collisions occur Some particles are super fast Some are super slow Most are “average” Collisions exert pushes

As the molecules move they collide Molecules collide with each other with energy being transferred Molecules collide with sides of container Newton’s 3rd law: action/reaction

How gases exert pressure Molecules collide and “push off” the container Each push is a force Force is over an area Pressure = F/A Pressure units:

Handling the pressure Common units: psi, kPa, atm, torr, mm Hg Measured with a barometer Closed-end barometer Open-end barometer

Calculating pressures from barometric data For a closed-end barometer (manometer): the pressure is the difference between Hg levels For a open-end barometer: the pressure is the atmospheric pressure + the difference in the columns of Hg