Gases Describing Gases

Review of Kinetic Theory Particles in an ideal gas… gases are hard, small, spherical particles don’t attract or repel each other. are in constant, random, straight-line motion. indefinite shape and volume. have “perfectly” elastic collisions.

Variables that describe a gas Units Pressure (P) – kPa, mm Hg, atm, torr L , mL , cm3 Volume (V) – °C , K (convert to Kelvin) K = °C + 273 Temp (T) – Mole (n) - mol

Gas Pressure - collision of gas molecules with the walls of the container Atmospheric Pressure- collision of air molecules with objects

Which shoes create the most pressure? Which create the least? Why?

Gas Pressure -- 3 ways to measure pressure: atm (atmosphere) mm Hg kPa (kilopascals) 1 atm = 760 mm Hg = 101.3 kPa U-tube Manometer How can we make these into conversion factors?

Atmospheric pressure is measured with a barometer. Increase altitude – decrease pressure Ex. Mt. Everest – atmospheric pressure is 253 mm Hg Vacuum- empty space with no particles and no pressure Ex: space

Gases Kelvin Temperature Scale is directly proportional to the average kinetic energy, so Temperature is a description of the movement of particles (not how hot or cold it is)

Standard Temperature and Pressure STP Standard Temperature and Pressure Standard pressure – 1 atm, 760 mm Hg, or 101.3 kPa Standard temp. – 0° Celsius or 273 Kelvin