Gas and Stoichiometry
ABCD of gas laws
Ideal gas law and Dalton's law of parial pressures
From the Ideal Gas law to Dalton's law
P V = n R T
= nTotal R T
= (n1 + n2 +
n3 + ...) R T
= (P1 + P2 +
P3 + ...)
Mole fraction of gas 1, X1
X1 = -----
A 1.0-L cylinder contains 0.5 g each of N2, O2
and CO2 at 273 K. Calculate the total pressure, partial pressure, and
See the table of results
|Gas ||Amount /mol ||P = n R T /atm ||Mole fraction
|N2 ||0.5/28 = 0.179 mol || P = 0.40 ||0.40
|O2 ||0.5/32 = 0.156 mol || P = 0.35 ||0.35
|CO2 ||0.5/44 = 0.114 mol || P = 0.254||0.25
Collecting Gases over Water
The vapour pressure of water is a function of temperature, and a plot
On July 1, the atmosphere pressure was 745 mmHg kPa at 30 C and the air is
saturated with water vapor, 31.8 mmHg. Estimate the mole fraction
of water vapour.
X = 31.8 / 745 = 0.043 (4.3 %)
The partial pressure of dry air would have been 745 - 31.8 = 713 mmHg.
Kinetic Theory of Gases
P V = N m u2/2
- Molecular size, attraction, & repulsion negligible
- Average kinetic energies of gases are the same at the same T
- Pressure due to kinetic energy
= (3/2) R T
u = (3 R T / N M)1/2
= (3 k T / M)1/2
M1 u12 = M2 u22.
-- = (---)2
The Graham's law of effusion is
k k '
rate of effusion = ------ = ------
- Ratio of effusion rates
- Balloon business
- Separation of isotopes
van Der Waals Equation
(P + (n/V)2 a) (V - nb) = n R T
nb - Volume of n moles molecules.
(n/V)2 a - Pressure correction term.