2 Ludwig Boltzman and James Maxwell They each proposed a model to explain the properties of gases.This model is called, kinetic-molecular theory because all of the gases known to them contained molecules.The word kinetic means “to move” and objects in motion have kinetic energy.
4 The Kinetic-Molecular Theory Describes the behavior of gases in terms of particles in motion.This model makes several assumptions about the size, motion, and energy of gas particles.
5 Particle SizeGases consist of small particles that are separated from one another by empty space.Gas particles are far apart, so there is no significant attractive or repulsive forces among them.
6 Particle Motion Gas particles are in constant random motion. Particles move in a straight line until they collide with other particles or with the walls of their container.Collisions between gas particles are elastic, meaning that no kinetic energy is lost.Kinetic energy can be transferred between colliding particles, but the total energy of the particles does not change.
7 Particle Energy2 factors determine the kinetic energy of a particle. Mass and VelocityAll particles do not have the same velocity but have the same mass.
9 Low Density Density is mass per unit volume The kinetic-molecular theory states a great deal of space exists between gas particles
10 Compression and Expansion When a gas is compressed the particles get closerWhen a gas expands there is more air space
11 Diffusion and Effusion There are no significant attractions between gas particlesThe mixture of gases in the air diffuse until they are evenly distributedThe rate of diffusion depends mainly on the mass of particles involvedMass of a gas varies from gas to gas
12 Diffusion and Effusion cont. During effusion a gas escapes through a tiny openingThomas Graham did experiments to measure the rates of effusion for different gases at the same temperature
13 Diffusion and Effusion cont. Grahams law of effusion states that the rate of effusion for a gas is inversely proportional to the square root of its molar massGrahams law also applies to rates of diffusion
14 GAS PRESSURE PRESSURE: FORCE PER UNIT AREA EX: Water Striders, snowshoes
15 MEASURING AIR PRESSURE TOOLS:BAROMETER: MEASURES ATMOSPHERIC PRESSUREMANOMETER: MEASURES THE PRESSURE OF A GAS IN A CLOSED CONTAINER
16 UNITS OF PRESSURE Pascal: N/m^2 (SI unit of pressure) COMPARED TO ATMKILOPASCAL (kPa)1 atm = kPaMILLIMETERS OF MERCURY (mm Hg)1 atm = 760 mm HgTORR1 atm = 760 torrPOUNDS PER SQUARE INCH (lb./in^2) or (psi)1 atm = 14.7 psiAtmosphere (atm)Pascal: N/m^2 (SI unit of pressure)Atmosphere: 760 mm Hg@ sea 0 degrees C
17 Dalton’s Law of Partial Pressures The total pressure of a mixture of gases is equal to the sum of the pressures of all the gases in the mixture.Ex: P (gas 1) + P (gas 2) = P (total)