GASES
Characteristics of gases
 Gases are highly compressible and occupy the full volume of
the container they are in
 When a gas is subjected to increased pressure, its volume
decreases
 Gases always form homogeneous mixtures with other gases
Gas Laws
 Boyles Law
o The volume of a fixed quantity of gas , at constant
temperature, is inversely proportional to its pressure
o V = 1/P x constant
 Charles Law
o The volume of a fixed quantity of gas at constant
pressure is directly proportional to its absolute
temperature
o V = T x constant
 Avogadros Law
o Gay-Lussac: At a given temperature and pressure, the
volumes of gases that react with one another are ratios of
small whole numbers
o Avogadros hypothesis: Equal volumes of gases at the
same temperature and pressure contain the same number
of molecules
o Avogadros Law: The volume of a gas at constant
temperature and pressure is directly proportional to the
number of moles of gas. V = constant x n
o 22.4 L of any gas at 0 degrees C and 1 atm contain 6.02 x
1023 molecules
 The Ideal Gas Equation
o PV = nRT where R = 0.08206 L atm/mol K
o 1 mole of gas at STP( 0 degrees C, 273.15 K, 1 atm) is
22.4 L
o In general if we have a gas under 2 sets of conditions:
 P1 V1/ n1T1 = P2V2/ n2T2
 Gas density and molar mass
o M =dRT/P
 Gas mixtures and partial pressures
o Daltons Law of partial pressures: the total pressure of a
gas mixture is equal to the sum of the partial pressures of
each component
Kinetic Molecular Theory
 Gases consist of large numbers of molecules in constant
random motion.
 Energy is transferred during collisions, but average kinetic
energy is constant at constant temperature
 Average kinetic energy is proportional to absolute temperature
 Effects of an increase in volume(at constant temp)
o The average kinetic energy remains the same
o Pressure decreases( molecules have farther to go to hit
walls)
 Effects of increased temp(at constant volume)
o The average kinetic energy increases
o There are more collisions with the container
o Therefore, pressure increases
Grahams Law
 Average kinetic energy is related to mass (KE =1/2 MV2)
 So for 2 gases at the same temp, v will be proportional to the
mass. Lower mass molecules will move faster
 Effusion is the escape of gas molecules through a tiny hole into
an evacuated space
 Diffusion is the spread of one substance through space or
another substance