Gases

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.

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

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

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

Always use absolute temperature (Kelvin) when working with gases. ºF ºC K K = ºC + 273

Which shoes create the most pressure?

Barometer measures atmospheric pressure Mercury Barometer Aneroid Barometer

Manometer measures contained gas pressure U-tube ManometerBourdon-tube gauge

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

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

In 1662, Robert Boyle discovered that the volume of a gas is inversely proportional to its pressure (at constant temperature). P V

P 1 V 1 = k P 1 V 1 = P 2 V 2 P 1 V 1 = k = P 2 V 2 K is a constant and has units of L-atm

V T Charles discovered that the volume and absolute temperature (K) of a gas were related (at constant pressure).

V T The volume of gases extrapolates to zero at -273 o C or 0 K. When the gases exceed this point the volume calculation would suggest that the gases would have a negative volume.

V = bT V1T1V1T1 = b = V2T2V2T2 V1T1V1T1 V2T2V2T2 =

Pressure and Temperature are also proportional (at constant volume). By putting all relationships together, it forms the Combined Gas Law. P 1 V 1 T 1 P 2 V 2 T 2 =

In 1811, Avogadro proposed that equal volumes of gases contain equal numbers of particles (at same T, P) It followed that the volume of a gas is proportional to the number of moles. V1n1V1n1 V2n2V2n2 = V = na V1n1V1n1 = a = V2n2V2n2

V = na V = bT PV = k Boyle’s law Charles’s law Avogrado’s law At constant T and n At constant P and n At constant T and P Can be combined to form: PV = nRT R = L-atm/K-mol

The total pressure of a mixture of gases equals the sum of the partial pressures of the individual gases. P total = P 1 + P When a H 2 gas is collected by water displacement, the gas in the collection bottle is actually a mixture of H 2 and water vapor.