Physical Properties Ch. 10 & 11 - Gases

A. Kinetic Molecular Theory b Particles in an ideal gas… have no volume. have elastic collisions. are in constant, random, straight- line motion. don’t attract or repel each other. have an avg. KE directly related to Kelvin temperature.

Ideal Gases don ’ t exist b Molecules do take up space All matter has volume b There are attractive forces otherwise there would be no liquids

Ideal Gases b There are no gases for which this is true. b Real gases behave this way at high temperature and low pressure.

Ideal Gases b In this chapter we are going to assume the gases behave ideally b Does not really exist makes the math easier close approximation. b Assume particles have no volume b Assume no attractive forces between molecules

B. Real Gases b Particles in a REAL gas… have their own volume attract each other b Gas behavior is most ideal… at low pressures at high temperatures in nonpolar atoms/molecules

Real Gases behave like Ideal Gases b When the molecules are far apart b They take a smaller percentage of the space b Ignoring their volume is reasonable b This is at low pressure

Real Gases behave like Ideal gases when b Molecules are moving fast. b Molecules are not next to each other very long b Attractive forces can’t play a role. b At high temp. b Far above boiling point.

C. Johannesson C. Characteristics of Gases b Gases expand to fill any container. random motion, no attraction b Gases are fluids (like liquids). no attraction b Gases have very low densities. no volume = lots of empty space

C. Characteristics of Gases b Gases can be compressed. no volume = lots of empty space b Gases undergo diffusion & effusion. random motion

DiffusionDiffusion u Molecules moving from areas of high concentration to low concentration. u Perfume molecules spreading across the room. u Effusion - Gas escaping through a tiny hole in a container. u From high to low concentration u Both depend on the speed of the molecules

C. Johannesson D. Temperature ºF ºC K K = ºC b Always use absolute temperature (Kelvin) when working with gases.

E. Pressure Which shoes create the most pressure?

E. Pressure b Barometer measures atmospheric pressure Mercury Barometer Aneroid Barometer

E. Pressure b Manometer measures contained gas pressure U-tube ManometerBourdon-tube gauge

E. Pressure b KEY UNITS AT SEA LEVEL kPa (kilopascal) 1 atm 760 mm Hg 760 torr 14.7 psi

F. STP Standard Temperature & Pressure 0°C 273 K 1 atm kPa -OR- STP