Please pick up a copy of two problem sets Wet Gases problem set Gas Bulb Problems problem set.
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Transcript of Please pick up a copy of two problem sets Wet Gases problem set Gas Bulb Problems problem set.
Please pick up
a copy of two problem sets
• Wet Gases problem set• Gas Bulb Problems problem set
Gaseous Mixtures
Edward A. Mottel
Department of Chemistry
Rose-Hulman Institute of Technology
Gaseous Mixtures
Reading Assignment:• Zumdahl, Chapter 5.5, 17.4
Gas Mixtures• Mole fraction• Dalton's Law of Partial Pressures• Vapor pressure • Wet gases
Atmospheric Composition
Dry air
78% N2, 21% O2, 1%Ar Normal air
N2, O2, Ar, 0.03% CO2, 1.6% H2O
Mole Fraction
The ratio of moles of a compound in a mixture to the total moles in the mixture.
A= + + +mol
mol mol molA
A B C ...
A gas sample contains 3 moles of hydrogen and 2 moles of oxygen.
What is the mole fraction of each gas?
Mole Fraction
H2
=moles H2
moles H2 + moles O2
=3
3 + 2= 0.60
O2
=moles O2
moles H2 + moles O2
=2
3 + 2= 0.40
The sum of the mole fractions in a mixture
equals exactly 1
Partial Pressure
The pressure a fixed amount of gas would exert if it were alone in a given volume at a given temperature.
Gas Bulb3 liters, 2 atm 2 liters, 1 atm
What will happen when the stopcock is opened?
Gas Bulb3 liters, 2 atm 2 liters, 1 atm
What will be the pressure of the orange atoms?
Hint: Use Boyle’s Law
Gas Bulb3 liters, 2 atm 2 liters, 1 atm
P · V = constant
2 atm · 3 L = 6 L· atm
Porange · 5 L = 6 L· atm
Porange = 1.2 atm
Partial pressure
Dalton's Law of Partial Pressures
The total pressure of a non-reacting gaseous mixture is the sum of the partial pressures of each gas in the mixture.
Ptotal = PA + PB + PC + ...
Gas Bulb3 liters, 2 atm 2 liters, 1 atm
What is the total pressure in the left bulb?
1.6 atm
What is the total pressure in the right bulb?
1.6 atm
Dalton's Law of Partial Pressures
What is the mole fraction of each gas?
PA = Ptotal · A
What is the partial pressure of each gas?
Vapor Pressure
The pressure exerted by the vapor of a substance when in equilibrium with the substance.• Even below their boiling point, liquids
evaporate or vaporize and solids sublime.
Vapor Pressure
• If a container is closed, then only a certain amount of liquid will evaporate until the air is saturated with the vapor.
Adding additional liquid does not increasethe amount of vapor in the air.
Vapor Pressure
• Boiling occurs when the vapor pressure of a liquid equals or exceeds the restraining pressure (e.g., atmospheric pressure)
Is it possible forwater to boil at room
temperature?
Vapor Pressure of Water
0
20
40
60
80
100
0 10 20 30 40 50
Temperature (°C)
Pre
ssu
re (
torr
)
Increases non-linearly with increasing temperature.
Wet GasesGases trapped byliquid displacement.
P P Ptotal gas water vapor= +
Is the pressure of the trapped gas equal to,less than or greater than atmospheric pressure?
Common GasesRoom Temperature, One Atmosphere Pressure
Monatomic: He, Ne, Ar, Kr, Xe, Rn Polyatomic
• Elements: H2, N2, O2, O3, F2, Cl2• Compounds: CO, CO2, NO, N2O, NO2,
N2O4, N2O5, CH4, C2H6, C2F4, etc.