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GASES AND KINETIC MOLECULAR THEORY (Osmotic pressure (Colligative…
GASES AND KINETIC MOLECULAR THEORY
Distinction of gases
Volume changes greatly with pressure and temp
Relatively low viscosity
Relatively low densities
Miscible - can mix
Units
1 atm = 760 mmHg
1 torr = 1 mmHg
1 bar = 100kPa
Gas laws
Avogadro's law
Volume of a gas at constant temp and pressure is directly prop to number of moles of the gas
V1 / n1 = V2 / n2
Boyle's law
Volume of gas is inversely prop to pressure exerted by gas if number of moles and temp of gas are constant
P1V1 = P2V2
Charles' law
Volume of gas directly prop to absolute temp (K) if pressure and number of moles of gas are constant
V1 / T1 = V2 / T2
Combined gas law
V = constant x T / P
Dalton's law
Mixture of gases exerts a pressure that is sum of pressures
Mole fraction X = amount (mol) of X / amount (mol) total
Ptotal = P1 + P2 + P3 +...
P1 = X1 x Ptotal
Postulates of KMT
Particle volume
Volume of gas particle so small compared to container we don't consider it (gas particles have mass but no volume)
Particle collisions
Elastic so total kinetic energy of particles constant
Intermolecular interactions
No force of attraction between particles or walls of container
Particle motion
Constant, random, straight line motion except when colliding with each other or container wall
Gas temperature and Ek
Av. Ek of collection of particles depends on temp of gas
Avogadro's law
For given amount, n1, of gas, Pgas = Patm
When gas is added to reach n2, collision frequency of particles increase, so Pgas > Patm
As a result, V increases until Pgas = Patm again
Boyle's law
At any T, Pgas = Pext as particles hit walls from av. distance, d1
Higher Pext causes lower V, which results in more collisions, because particles hit walls from shorter av distance (d2 < d1) until, Pgas = Pext again
Charles' law
At T1, Pgas = Patm
Higher T increases collision frequency, so Pgas > Patm
V increases until Pgas = Patm at T2
Distribution of molecular speeds at 3 temps
Graph on slides
Ek directly prop to T (absolute) so at a given temp all gases have same av. Ek
As T increases, av. Ek increases so av. speed of molecules increases
Diffusion
Dispersion of 1 substance through another
Effusion
Escape of 1 substance through small hole into vacuum
Rate directly prop to 1 / √M
Effects of pressure on gas solubility
Increase in pressure = decrease in volume = more collisions with surface so more go into solution
Equilibrium: gas out of solution = gas in solution
Henry's law
Solubility of gas (Sgas) directly prop to the partial pressure of gas (Pgas) above solution
Sgas = kH x Pgas
Any given partial pressure of gas, solubility will be inversely prop to temp
Osmotic pressure
Colligative properties
Depend on number of solute particles, not chemical indentity
Number of particles in solution can be predicted from formula and type of solute
Particles can be molecules or ions
Electrolytes
Separates into ions when dissolved in water
Strong dissociate completely, weak dissociate incompletely
Non electrolytes
Don't dissociate
Each mole yields 1 mole
Osmosis: movement of solvent particles through semi permeable membrane from region of higher conc to region of lower conc
"Colligative property and is equal to pressure that must be applied to prevent net flow of solvent
π(pressure)V = nRT