Gases Properties Kinetic Molecular Theory Variables The Atmosphere Gas Laws

Properties of a Gas No definite shape or volume Gases expand to fill any container Thus they take the shape of the container, as well as the volume! Low Density Most of the volume of a gas is empty space-since the gas particles want to be as far from all like particles as possible As a result, gases are compressible

Properties of a Gas Fluid can flow like a liquid

The Atmosphere Composed of a mixture of gases -Approx. 80% N 2 and 20% O 2 Provides conditions for life, protects from UV radiation, traps heat Please read about the Greenhouse Effect and the Ozone Layer in your text books…you will be responsible for that information...

The Kinetic Molecular Theory Explains the behavior of gases at the molecular level Based on assumptions about a theoretical gas referred to as the Ideal Gas.

The Kinetic Molecular Theory 1) Volume of gas particles is essentially zero (Point Masses) 2) Particles are in constant, random motion 3) No attractive forces betw. particles and collisions are perfectly elastic No energy is lost by the particles during collisions

The Kinetic Molecular Theory 4) The temperature of a gas is directly proportional to the average kinetic energy associated with the particles, thus the higher the temperature, the faster the particles are moving... K.E. = 1/2 mv 2

Ideal vs. Real Gas Ideal Gas Has mass but no volume Has no attractive forces between molecules Real Gas Molecules do have volume Molecules exert an attractive force on each other when very close.

Ideal vs. Real Gas At normal temps. & pressures, real gases behave like ideal gases

Four variables that describe a gas... 1) Temperature - the measure of the avg. kinetic energy gases at the same temp. must have the same avg. kinetic energy Must be in Kelvin! T K = T C + 273

Four variables that describe a gas... 2) Volume - The amount of space occupied by the particles, measured in liters, mL, cm 3, m 3, etc.

Four variables that describe a gas... 3) Pressure - The force exerted by the gas per unit of area In gases - meas. of total force exerted by the particles colliding w/ the walls of their container. - proportional to the number of collisions -Incr. temp, incr. press. - Incr. # of particles, incr. press. usually measured in: atmospheres (atm), kPa (kilo-pascals), N/m 2 Pascal - SI unit of pressure = to 1 N/m 2 very small press. - usually use kilopascals

Four variables that describe a gas... 4) Number of particles Equal volumes of gases under the same conditions have equal numbers of particles...

Avogadro’s Principle The volume of a gas at a given temperature and pressure is directly proportional to the number of moles of that gas ie equal volumes of gases under the same conditions contain the same number of particles. Molar Volume is the volume of 1 mole of any gas at STP

Standard Conditions STP Standard Temperature is 273 K Standard Pressure is… atm kPa mm Hg torr Note: you can use any pressure units but you can only use Kelvin temperature units!

The Gas Laws Boyle’s Law - the volume of a gas at constant temp. is inversely proportional to the pressure P 1 V 1 = P 2 V 2 Read Ch. 12 Section 2

The Gas Laws Charles’ Law - the volume of a gas at constant press. is directly proportional to the absolute (Kelvin) temp. V 1 / T 1 = V 2 / T 2

The Gas Laws Combined Gas Law - Combines Boyle’s & Charles’ Law P 1 V 1 / T 1 = P 2 V 2 / T 2 Read Ch. 12 Section 2

The Gas Laws Ideal Gas Law PV = n R T n = # of moles R = 8.31 L kPa / mol K Or L atm / mol K Read Ch. 12 Section 2