Kinetic Theory of Gases
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1
Kinetic Theory of Gases
consists of small particles thatmove rapidly in straight lines.
essentially no attractive (or repulsive) forces.
are very far apart.very small volumes compared
volume of container occupied kinetic energies
increase with increased temperature.
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Properties that describe a gas
four properties: pressure (P), volume(V), temperature(T), and amount(n).
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What is gas pressure?
force acting on a specific area. Pressure (P) = Force
Areaunits of atm, mm Hg, torr
1 atm = 760 mm Hg1 atm = 760 torr
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What is atmospheric pressure?
pressure exerted by a column of airfrom top of atmosphere
to surface of earth1 atmosphere at sea leveldepends on altitude and weatherlower at high altitudes
density of air less. higher on a rainy day
than sunny day
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What is a barometer?
measures pressure exerted by gases in atmosphere.
indicates byheight in mm of mercury column.
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Boyle’s Law (pressure-volume) law
pressure of a gas inversely related to its volumewhen T and n are constant
volume decreasespressure increases
product P x V constant as long as T and n unchanged
P1V1 = P2V2 (T, n constant)can be solved for any factor
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Breathing, an example
During inhalation lungs expandpressure in lungs decreasesair flows towards lower pressure in
lungsDuring exhalation
lung volume decreasespressure within lungs increasesair flows from higher pressure in
lungs to outside
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Calculation with Boyle’s Law
Freon-12, CCl2F2, is used in refrigeration
systems. What is the new volume (L) of a 8.0
L sample of Freon gas initially at 550 mm Hg
after its pressure is changed to 2200 mm Hg at
constant T?1. Set up a data table:
Conditions 1 Conditions 2
P1 = 550 mm Hg P2 = 2200 mm HgV1 = 8.0 L V2 =
?
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Calculation with Boyle’s law (continued)
2. When pressure increases, volume decreases.Solve Boyle’s Law for V2: P1V1 = P2V2
V2 = V1 x P1
P2 V2 = 8.0 L x 550 mm Hg = 2.0 L
2200 mm Hg
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Learning Check
For a cylinder containing helium gas
indicate if cylinder A or cylinder Brepresents the new volume for thefollowing changes (n and T areconstant).
1) pressure decreases2) pressure increases
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Learning Check
A sample of oxygen gas has a volume of
12.0 L at 600. mm Hg. What is the new
pressure when the volume changes to
36.0 L? (T and n constant).
A) 200. mm Hg B) 400. mm Hg C) 1200 mm Hg
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Solution A) 200. mm Hg
Data table Conditions 1 Conditions 2P1 = 600. mm Hg P2 = ???V1 = 12.0 L V2 = 36.0 L
P2 = P1 x V1 V2
= 600. mm Hg x 12.0 L 36.0 L = 200. mm Hg
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Charles’ law temperature -volume
Charles’ Law,Kelvin temperature of a gas
directly related to volume P and n are constanttemperature of a gas increases
volume increasesV1 T1= V2 T2
(P and n constant)rearranging Charles’ Law
Calculations using charles’ law
A balloon has a volume of 785 mL at21°C. If the temperature drops to
0°C, what is the new volume of the balloon(P constant)? 1. Set up data table:Conditions 1 Conditions 2V1 = 785 mL V2 = ?T1 = 21°C = 294 K T2 = 0°C =
273 KKelvin (K) temperature in gas
calculations.
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Calculations Using Charles’ Law (continued)
2. Solve Charles’ law for V2:
V1 = V2
T1 T2
V2 = V1 x T2
T1
V2 = 785 mL x 273 K = 729 mL 294 K
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Learning Check
A sample of oxygen gas has a volume of
420 mL at a temperature of 18°C. At
what temperature (in °C) will thevolume of the oxygen be 640 mL
(P andn constant)?
1) 443°C2) 170°C 3) - 82°C
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What is STP?
volumes of gases can be compared at STP, Standard Temperature andPressure,
the same temperature.Standard temperature (T) 0°C or 273 K
the same pressure. Standard pressure (P) 1 atm (760 mm Hg)
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What is Molar volume?
standard temperature and pressure (STP), 1 mole of a gas occupies a volume of 22.4 L, its molar volume
used to form conversion factors22.4 L and 1 mole 1 mole 22.4 L
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Partial Pressure (Dalton’s Law) pressure of each gas in mixture. pressure gas would exert if
itself in container pressure depends on total number of gas
particles not on types of particles
total pressure exerted by gases mixture sum of partial pressures of gases
Calculate the sum of the partial pressures.Ptotal = PO2 + PHe
Ptotal = 342 mm Hg + 855 mm Hg
= 1197 mm Hg
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Scuba Diving-!When a scuba diver dives,
increased pressure causes N2(g) to dissolve in blood.
If diver rises too fast, dissolved N2 will form bubbles in
blood"the bends"
Helium, does not dissolve in blood, mixed with O2 to prepare breathing
mixtures for deep descents.
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Gases We Breathecontains N2 and O2 & smallamounts of other gasesO2 enters blood, while CO2 from
blood releasedtissues, O2 enters cells,
release CO2 into blood. O2 flows into tissues
partial pressure of O2 higher in blood, lower in tissues
CO2 flows out of the tissues partial pressure of CO2 is higher in tissues, lower in the blood