Thursday
February 2, 2012
(Dalton’s Law of
Partial Pressures;
Avogadro’s Law)
A sample of chlorine gas (Cl2) is at a
temperature of 750C and is occupying a
volume of 750. mL. If the temperature is
increased to 980C, what will the resulting
volume be? By what law?
800. mL
Charles’ Law
Date Into
Grade
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Last Day
1/24
2/7
1/27
1/27
2/10
1/30
2/1
Assignment Currently
Open
Summative or
Formative
Date
Issued
Date
Due
WS: Stoichiometry – Mole to Mole
Conversions
F3
1/6
1/10
WS: Chart It! Think-Pair-Share (Part 1)
F4
1/9
1/11
F5
1/10
1/12
F7
1/12
1/19
S2
1/20
1/20
Activity – Stoichiometry, Limiting
Reactant, and Percent Yield – Putting It
All Together
1/23
1/24
WS – Introduction to Gases
1/24
1/26
1/23
1/27
1/27
WS: Chart It! Think-Pair-Share (Part 2)
The Mathematics of Combustion Reactions
OR
The Mathematics of CO2 Scrubbers
QUIZ – LIMITING REACTANT & PERCENT
YIELD
Bell Ringers 1/23 thru 1/27
F
QUIZ – THE NATURE OF GASES
WS - Pressure
F
WS – Boyle’s Law
F
1/31
2/2
WS - Charles’ Law
F
2/1
2/3
Announcements
I will be available this
afternoon after school until
5:00.
The Gas Laws
• Boyle’s Law
pressure – volume relationships
• Charles’s Law
volume - temperature relationships
• Dalton’s Law of Partial Pressures
partial pressures and total pressures
Dalton’s Law of
Partial Pressures
John Dalton, the English
chemist who proposed the
atomic theory, also studied
gas mixtures.
He found that in the
absence of a chemical
reaction, the pressure of a
gas mixture is the sum of
the individual pressures of
each gas alone.
Dalton’s Law of
Partial Pressures
This picture shows a 1.0 L container filled
with oxygen gas at a pressure of 0.12 atm
at 0°C.
In another 1.0 L container, an equal
number of molecules of nitrogen gas
exert a pressure of 0.12 atm at 0°C.
The gas samples are then combined in a
1.0 L container. (At 0°C, oxygen gas and
nitrogen gas are unreactive.)
The total pressure of the mixture is found
to be 0.24 atm at 0°C.
The pressure that each gas exerts in the
mixture is independent of that exerted by
other gases present.
The pressure of each gas in a mixture is
called the partial pressure of that gas.
Dalton’s Law of Partial Pressures
Dalton’s law of partial pressures states that the
total pressure of a mixture of gases is equal to the
sum of the partial pressures of the component
gases.
The law is true regardless of the number of
different gases that are present.
Dalton’s law may be expressed as follows:
PT = P1 + P2 + P3 + . . .
PT is the total pressure of the mixture. P1, P2 , P3,
. . . are the partial pressures of component gases 1,
2, 3, and so on.
Dalton’s Law of Partial Pressures
Sample Problem
Three of the primary components of air are carbon dioxide,
nitrogen, and oxygen. In a sample containing a mixture of
only these three gases at exactly one atmosphere pressure,
the partial pressures of carbon dioxide (PCO2) = 0.285 torr and
nitrogen (PN2) = 593.525 torr. What is the partial pressure of
oxygen?
PT = P 1 + P 2 + P 3 + . . .
Pair = PCO2 + PN2 + PO2
Pair = 1 atm = 760.000 torr
760.000 torr = 0.285 torr + 593.525 torr + PO2
PO2 = 760.000 – 0.285 – 593.525 = 166.190 torr
Avogadro’s Law
In 1811, Amedeo Avogadro hypothesized that two given
samples of an ideal gas, of the same volume and at the
same temperature and pressure, contain the same number
of molecules.
Thus, the number of molecules or atoms in a specific volume
of gas is independent of their size or the molar mass of the
gas.
As an example, equal volumes of
molecular hydrogen and nitrogen contain the same number
of molecules when they are at the same temperature and
pressure, and observe ideal gas behavior.
Avogadro’s Law
Consider the reaction of hydrogen and chlorine to produce
hydrogen chloride.
According to Avogadro’s law, equal volumes of hydrogen and
chlorine contain the same number of molecules.
H2
1 volume
1 molecule
+
Cl2 →
1 volume
1 molecule
2HCl
2 volumes
2 molecules
Avogadro’s Law
Avogadro’s law also indicates that gas volume
is directly proportional to the amount of gas, at
a given temperature and pressure.
Note the equation for this relationship.
V = kn
Here, n is the amount of gas, in moles, and k is
a constant.
Worksheet
Dalton’s Law (Partial Pressures)
Avogadro’s Law (Same V,T,&P
– Same Number of Molecules)