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KINETIC MOLECULAR THEORY
KINETIC MOLECULAR THEORY
there are _ Posutlates
5
The postulates are:
gas particles are in constant motion
the combined volume of the particles of gas sample is negative compared to the volume of a container
there are no attractive forces between the particles of a gas sample (so we assume)
collisions between the gas particles ate completely elastic (meaning no energy is used)
the average kinetic energy of gas particles in a sample is directly proportional to the kelvin temperature
Pressure =
force applied over a specific area
Why do gas particles exert pressure?
in constant motion, the particles collide with the walls of the container
How can we increase pressure?
increase temperature
decrease volume of the container
add more gas particles
Units for pressure
atm = atmosphere (of pressure)
Kpa = kiloPascal
mmHg = millimeter of Mercury (torr)
psi = pounds per square inch (tire pressure)
STP VALUES
1 atm = 101.3 kPa = 760 mmHg(torr)
How many atm is 252 kPa?
252 kPa x 1 atm/101.3 kPa = 2.49 atm
BOYLE’S LAW
BOYLE’S LAW
Boyle’s law =
the relationship between pressure and volume
inversely proportional relationship
Equation = P1V1 = P2V2
example
P1V1 = P2V2
(103.1kPa)(1.00L) = P2 (0.35L)
divide both sides of 0.35L
P2 = 295 kPa
CHARLES’S LAW
relationship between temperature and volume
directly proportional relationship
Equation = V1/T1 = V2/T2
Temperature Must be in..
Kelvin (because it does not have any negative numbers)
To convert celsius to Kelvin…
add 273 to the celsius
Gay-Lussac’s Law
relationship between pressure and temperature
directly proportional relationship
Equation = P1/T1 = P2/T2
Temp must be in kelvin
Combined Gas Law
looks at relationship between pressure,volume, and temperature when all 3 values are changing
Equation = P1V1/T1 = P2V2/T2
STP =
1 atm, O degrees Celsius, 273 kPa
The Ideal Gas Law
no change in conditions
Equation = PV = nRT
R = gas law constant
n = number of moles
IDEAL GAS LAW CONSTANT
0.08206 L x atm/mol x K
8.314 L x kPa/mol x K
62.36 L x torr/mol x K
To calculate the number of moles to grams it is…
number of moles (n) x molar mass/1 mole
Avogradro’s Law
relationship between volume and moles of a gas
directly proportional relationship
Equation = V1 / n1 = V2 / n2
n =
moles of a substance
Dalton’s Law of Partial Pressures
The total pressure of a mixture of gases is the sum of the partial pressures of each component
P total = Pa + Pb + Pc + …
Notes about Dalton’s Law
most gas samples are mixtures
Air → Mixture
O2, N2, CO2, H2O, others
The pressure due to any one of those components in the mixture is called…
partial pressure
Partial pressure of any component =
mole fraction x P total
Mole Fraction =
Xn
(the X is a little curvy on the top left corner and bottom right corner)
EXAMPLE
EXAMPLE
What fraction of the total moles of the mixtures comes from each component?
mixture of O2, H2, N2
3 moles O2, 4 moles H2, 4 moles N2
XO2 = 3/11
XN2 = 4/11
XH2 = 4/11
The total pressure of the mixture above is 122.5 KPa
122.5 KPa = P total
Calculate the partial pressure of O2
The Partial Pressure of any component equals the mole fraction of that component times the total pressure
PO2 = XO2 x Ptotal
= 3/11 × 122.5 KPa
= 33.4 KPa
In the mole ratio of O2 (3/11)…
the 3 is the number of moles of the component
the 11 is the moles added
(ex: 4 + 4 + 3 = 11)
Graham’s Law of Effusion
relates the speed at which a gas moves to its molar mass
Inverse Relationship (not proportional)
Equation =
speed of Gas A/ Speed of Gas B = √M.M of B/ M.M. of A
Heavier =
Lighter =
heavier = slower
lighter = faster
(higher molar mass = lower speed)
(lower molar mass = faster speed)
Gases move in _ ways
2
One way Gases Move: Effusion
the movement of gas particles escaping from a small hole in a container
Second way Gases move: Diffusion
movement from an area of high concentration to low concentration
Example of Graham’s Law
X/H2
(1/50)2 = (√2.02/x)2
1/2,500 = 2.02/x
x = 5,050 g/mol