9.5
Partial pressure and Dalton s Law
partial pressure - pressures that gases A and B would exert if they were alone
consider of mixture of gases: N2 and O2
The total pressure exerted by the mixture= Ptot = PA + PB
where PA = partial pressure of O2
PB = partial pressure of N2
assuming each gas behaves like an ideal gas, then
PA = partial pressure of A = nART
V
PB = partial pressure of B = nBRT
V
now Ptot = ntotRT = nART + nBRT
V
V
V
= (nA + nB)RT
V
In a mixture of gases the total pressure, Ptot , is the sum of the partial pressures
of the gases and is related to the sum of the moles of all gases
P total
RT
V
where
n is the sum of the
n moles of all gases in the mixture
Mole Fraction - fraction of total number of moles that is accounted for by a
particular gas.
n A = XA
ntot
where XA is the mole fraction in the gas A in mixture
PA = XAPtot
this equation allows you to calculate partial pressures using mole
fractions
1
PROBLEMS
1. A 5.0 L flask at 25 0C contains N2 at a partial pressure of 0.28 atm, He at a
partial pressure of 0.12 atm and Ne at a partial pressure of 0.56 atm.
What is the mole fraction of each gas?
2. What is the mole fraction of each component in a mixture of 12.45 g of H2
60.67 g of N2 and 2.38 g of NH3 ?
What is the total pressure (in atm) if the gas mixture is in a 10.00 L container
at 90 0C ?
9.6 Kinetic- Molecular Theory of Gases
This theory presents physical properties of gases in terms of the motion of individual
molecules.
- Average Kinetic Energy Kelvin Temperature
- Gas molecules are points separated by a great distance
- Particle volume is negligible compared to gas volume
- Gas molecules are in rapid random motion
- Gas collisions are perfectly elastic
- Gas molecules experience no attraction or repulsion
Average Kinetic Energy (KE) of a gas is given by:
KE
1
mu 2
2
where u is the average velocity of the gas
2
Lecture 30 is the last of my lecture notes to be placed on the
web.
Lectures 31 and 32 will be spent reviewing the course by
going over a copy of an old Final Chem 1010 Exam
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