Kinetic Molecular Theory of Gases

Spring 2016

KMT1. Gas particles are very small and

very far apartSize of a gas molecule is negligible in comparison to the distance between gas moleculesIn a sample of gas, most of the sample consists of empty space

KMT2. Gas particles move randomly in

straight-line paths in all directions and different speedsIn a sample of gas, there is an equal probability of finding gas particles w/ similar properties anywhere in a sampleAll particles will never be on the same side of a closed flask

KMT3. Attractive or repulsive

forces (interparticle forces or IMF’s) between gas particles are considered very weak or negligibleBecause particles are moving quickly and are far apart

KMT4. When gas particles do collide

the collisions are elasticDef: elastic collision – one in which the particles bounce off each other in such a way the energy is the same after the collision as before itNo Kinetic energy is lost

Kinetic Molecular Theory

KMT5. Average KE of a molecule

is proportional to the absolute temperatureAny two gases at the same temp will have the same KE

http://www.epa.gov/eogapti1/module1/kinetics/animation/kani1/kani102.htm

KMTThese thermometers compare the three common temperature scales.

Celsius Kelvin

K = C + 273.15All temperatures

must be in K!

Standard Pressure- Measured by the number of

collisions of gas particles with the container walls

- 1 atmosphere (atm) = 101.325 kilopascal (kPa) = 101325 pascal (Pa) =760 millimeters mercury (mmHg)=760 Torr

doIhaftawritethesedown?No!ReferenceTables!!

Barometer- Used to

measure the atmospheric pressure

BarometerThe mercury column rises and falls with changes in atmospheric pressure.

A direct relationship!!!

BarometerUnits are typically

mm Hg (SI) or

in Hg (English)

Manometer- Used to measure

difference between atmospheric pressure and gas pressure

ManometerLaboratory instrument used to measure pressure

An unknown pressure is the sum of atmospheric pressure and the column height

ManometerIn this example, Pgas < Patm , so the column height is -132 mm.

Pgas = Patm – 132 mm

The Gas LawsAvogadro’s LawBoyle’s LawCharles’ LawGay-Lussac’s LawCombined Gas LawIdeal Gas LawDalton’s Law of Partial Pressures

The Gas Laws – a recapThe Law

Avogadro

Boyle

CharlesGay-Lussac

VP T n Rel’shipDirect

Inverse

Direct

Direct