Drill 4/16/2015 What do you think is the oldest form of human
flight? How does it work?
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SWBAT Use the law of partial pressures to calculate partial
pressures and total pressures of gases. Use Boyles Law to calculate
volume-pressure changes at constant temperature. Use Charles Law to
calculate volume-temperature changes at constant pressure.
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Agenda Law of Partial Pressures Boyles Law Charles Law Online
Lab
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Think About It What do you already know about gases? List 3
things you think you already know about gases. What pressure units
used in gas measurements are you already familiar with? think about
everyday practical instances for example, the weather on the local
news or the pressure in a car tire
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Common Units of Pressure atm (atmosphere) torr mm Hg inches Hg
pascal (Pa) kilopascal (kPa) lb/in 2
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Conversions 1 atm = 101,325 Pa (pascals) = 101.3 kilopascals
(kPa) 1 atm = 760 mm Hg = 760 torr 1 atm = 14.70 lb/in 2 1 bar =
100,000 Pa = 0.9869 atm
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Practice Problem The column of mercury in a barometer is 745 mm
above the mercury reservoir at the bottom. What is the atmospheric
pressure in pascals (Pa)?
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Answer 99,325 Pa
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To Try on Your Own... The air pressure inside the cabin of an
airplane is 8.3 lb/in 2. What is this pressure in atmosphere
units?
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Answer 0.56 atm
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The Gas Laws: Boyles Law & Charles Law
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Kinetic-Molecular Theory Based on the idea that particles of
matter are always in motion. Explains the three states of matter A
model to explain the behavior of gases.
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Kinetic-molecular Theory Particles in a gas sample are far
enough apart that size has little influence on its volume.
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Measuring Gases In order to describe a gas sample and make
predictions about its behavior under different conditions, four
variables are used: 1.amount of gas, 2. volume, 3. temperature, and
4. pressure.
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Law of Partial Pressures The total pressure of a gas mixture is
the sum of the pressures of the gases in the mixture. P T = P 1 + P
2 + P 3 +...
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Sample Problem What is the atmospheric pressure if the partial
pressures of nitrogen, oxygen, and argon are 604.5 mm Hg, 162.8 mm
Hg, and 0.5 mm Hg, respectively?
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Answer 767.8 mm Hg
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Your Turn A mixture of O 2, CO 2 and N 2 has a total pressure
of 0.97 atm. What is the partial pressure of O 2 if the partial
pressure of CO 2 is 0.70 atm and the partial pressure of N 2 is
0.12 atm?
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Answer 0.15 atm
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Boyles Law the pressure and volume of a fixed mass of gas at
constant temperature are inversely proportional to each other P 1 V
1 = P 2 V 2 (equation form)
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Sample Problem A gas at a pressure of 608 mm Hg is held in a
container with a volume of 545 cm 3. The volume of the container is
then increased to 1065 cm 3 without a change in temperature.
Calculate the new pressure of the gas.
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Answer 311 mm Hg
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Practice Problem A balloon filled with helium gas has a volume
of 500. mL at a pressure of 1 atm. The balloon is released and
rises in altitude, where the pressure is 0.5 atm. If the
temperature has remained the same, what volume does the gas occupy
at this height?
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Answer 1000 mL He
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Charles Law The volume of a fixed mass of gas at constant
pressure varies directly with the Kelvin temperature. V 1 T 2 = V 2
T 1 (equation form)
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Important When solving gas law-type problems, the temperature
value that you plug into the necessary equation must be in units of
Kelvin (NOT Celsius)
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Temperature Conversion To convert between Celsius and Kelvin: K
= C + 273 For example, 20C = 293 K Note: The Kelvin scale is not a
degree scale
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Sample Problem What will be the volume of a gas sample at 355 K
if its volume at 273 K is 8.57 L?
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Answer 11.1 L
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Practice Problem A sample of air has a volume of 140.0 mL at
67C. At what temperature would its volume be 50.0 mL at constant
pressure?
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Answer 121 K = - 152C
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The Combined Gas Law The combined gas law expresses the
relationship between pressure, volume, and temperature of a fixed
amount of gas (P 1 V 1 )/T 1 = (P 2 V 2 )/T 2 Or P 1 V 1 T 2 = P 2
V 2 T 1
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Practice Prob #1 A helium-filled balloon has a volume of 50.0 L
at 25C and 1.08 atm. What volume will it have at 0.855 atm and
10.0C?
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Answer 60.0 L He
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Practice Prob #2 A gas has a volume of 1.75 L at - 23C and
150.0 kPa. At what temperature would the gas occupy 1.30 L at 210.0
kPa?
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Answer 260. K or - 13C
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Practice Prob #3 A sample of oxygen that occupies 1.00 x 10 6
mL at 575 mm Hg is subjected to a pressure of 1.25 atm. What will
the final volume of the sample be if the temperature is held
constant?
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Answer 6.05 x 10 5 mL
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Avogadros Law Equal volumes of gases at the same temperature
and pressure contain equal numbers of particles. V 1 = V 2 n 1 n
2
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Ideal Gas Law An Ideal Gas follows the gas laws under all
conditions of temperature and pressure. This concept is used to
model gas behavior A Real Gas does exist and has intermolecular
forces, particle volume, and can change states.
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Ideal Gas Law Calculations made using the ideal gas law are
used to estimate experimental measurements. The ideal gas law is
the mathematical relationship among pressure (P), volume (V), the
number of moles of a gas (n), and temperature (T). PV = nRT
(equation form)
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The Gas Constant The constant R is known as the ideal gas
constant R = 0.0821 (L-atm)/(mol-K)
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Be Careful with Your Units P (must be in atm) V (must be in L)
T (must be in K)
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Sample Problem An engineer pumps 5.00 mol of carbon monoxide
gas into a cylinder that has a capacity of 20.0 L. What is the
pressure in kPa of CO inside the cylinder at 25C?
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Answer 619 kPa
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Practice Prob 2 What volume would be occupied by 0.657 grams of
hydrogen gas at a pressure of 2.01 atmospheres and a temperature of
35.0C?
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Answer 4.09 L H 2
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Drill # 163/13 &14/13 Convert 748 mm Hg to atm. 0.984
atm
