Gas Properties and Laws Explains why gases act as they do.
Assumptions/Postulates of the theory 1. Gases are composed of small
particles. 2.These particles are in constant, straight-line, and
random motion. 3. Collisions between these particles are elastic
with each other. Nor do they exert attraction/repulsion on each
other. 4. The average kinetic energy of the gas molecule is
proportional to the temperature. Kinetic Molecular Theory: Basic
Concepts
Slide 4
1. Volume: Gas molecules can be compressed therefore one volume
is able to occupy a variety of volumes. Ex. How much CO 2 gas is in
a coke can? 2. Temperature: Since gases are free molecules, their
energy is important. The temperature can determine how the gas will
be or act. 3. Pressure: This affects gases a lot more than the
other 2 states of matter. This can also define how the gas will
act. That same amount will fill a trash can.
Slide 5
Force is the mass being applied. Pressure is the mass being
applied in a defined area. Pressure = Force/area Atmospheric
pressure: The amount of pressure being exerted by the mass of a
column of air over 1m 2 of space. Weather: Low pressure means it is
cloudy High pressure would be sunny
Slide 6
Gas pressure is how often the molecules of the gas collide with
the walls of its container. Barometers: this device is used to
measure atmospheric pressure. Simple Barometer: this is a glass
column going into a pool of mercury. As the atmospheric pressure
pushes down on the Hg pool, it causes some to rise or fall in the
column.
Slide 7
When using a barometer, the mercury level is measured in the
column. Thus the unit is mmHg The unit Torr is the same as mmHg The
SI unit is the Pascal (Pa). But Kpa is more commonly used. For gas
laws, the unit Atmospheres (atm) is used often. At sea level
1atm=101,325pa or 101.325kpa 760mmHg or 760torr 14.69lbs/in 2
Slide 8
Manometer: is a device that is used to determine the pressure
of a gas inside of a container. This device has a U-tube with a
specific amount of Hg in it. The container of gas is hooked up to
it and the gas is allowed to hit the Hg. The difference is the
levels of Hg on both sides tells you the pressure of the gas.
Closed ended: one end has a vacuum with a specific amount of
pressure in it. Open ended: the atmospheric pressure is used.
Slide 9
Manometers Open ended Closed ended
Slide 10
In a manometer problem; you need to know at least 2 of 3
variables. Manometer variables: 1. Pressure of container 2.
Pressure of atmosphere or vacuum 3. Height difference of Hg in tube
You must also be sure that the pressures are in the same unit as
the mmHg. You may need to do conversions.
Slide 11
1. A soccer ball is attached to an open-ended manometer. The
mercury level in the manometer is 10.0 mm higher on the side
attached to the ball than on the side open to the atmosphere.
Atmospheric pressure has already been determined to be 770.0 mm Hg.
What is the gas pressure in the ball?
Slide 12
2. A manometer contains a sample of nitrogen gas at a pressure
of 88.3 kPa. The level of mercury in the U-tube is 12.8 mm lower on
the end open to the atmosphere. What is the atmospheric pressure in
torr?
Slide 13
If you have an empty bottle is it really empty? (cap is off)
Any gas trying to be collected into that bottle will simply mix
with the other gases in air. Water displacement can be used to
collect gases with absence of air, but there will be a small amount
of water vapor. When you mix gases, each have a certain amount of
pressure. This is called a Partial Pressure. Daltons law of partial
pressure is for the total pressure of gases in a system. P total =
P a + P b + P c
http://www.wwnorton.com/chemistry/tutorials/interface.s
wf?chapter=chapter_08&folder=daltons_law
Slide 14
Boyles Law Boyle Law describes the volume-pressure
realationship. Boyle Law describes the volume-pressure
realationship. This is an inverse relationship: As you add
pressure, volume decreases. For this to happen though, temperature
must be constant. Boyle's Law.. Animated Boyles law is expressed
as: P 1 V 1 = P 2 V 2 Pressure units do not matter
Slide 15
If a bag of chips is filled with enough air to create a 1.5L
bag at 101.3kpa in Kansas City. What volume will the bag be if it
is taken to Denver at a pressure of 89.98kpa? Write Boyles law: P 1
V 1 = P 2 V 2 Next determine which numbers go together: 1.5L and
101.3kpa then ?L and 89.98kpa Finally substitute the numbers and
solve for x: (101.3kpa)(1.5L) = (89.98kpa)(?L) X = 1.69L
Slide 16
A 2.3L balloon is filled on the ground at 103.456kpa. The
balloon is then taken in a plane that has a pressure of 67.8kpa,
what is the volume of the balloon? A. 3.5L B. 1.5L C. 3049.7L D.
Can not be determined with this info
Slide 17
Kelvin scale of temperature: In the SI system, Kelvin is used
since it does not have negative values. Zero Kelvin is called
absolute zero. Zero Celsius = 273K Charless law is the direct
relationship between temp and volume of a gas As temp increases
Volume increases Charless Law equation: V 1 T 2 = V 2 T 1 ( T must
be in Kelvin) Charles and Gay-Lussac's Law - Animated
Slide 18
38c would be ______K A. -235 B. 311 C. 7
Slide 19
A volume of argon gas at the temperature of -10c occupies a
volume of 1L. What Celsius temperature will the gas need to be to
occupy a volume of 2.2L? 1 st you have to make sure all of your
temperatures are in Kelvin. So -10c + 273 = 263K Next write out
Charless equation: V 1 T 2 = V 2 T 1 Identify which temp and volume
go together and make them the 1s. The other variable then becomes
the 2s. So: (1L)(x) = (2.2L)(263K) X = 578.6K 578.6K 273 =
305.6c
Slide 20
A can of soda has a volume of 350ml at 25c, what volume would
it be if it was at 45c? A. 630mL B. 328.0mL C. 194.4mL D.
373.5mL
Slide 21
If you want a balloon to get bigger how do you make it bigger?
(pressure and temp are constant) Avogadros law is the direct
relationship of volume to quantity of particles. V = n where n =
moles So if you have 2 samples: V 1 n 2 = V 2 n 1 Increase
particles animated
Slide 22
From the information you have learned; what is the relationship
going to be between pressure and temperature? Direct or Indirect?
How will the equation look? P 1 T 2 = P 2 T 1 (T must be in Kelvin)
Gay-Lussacs Law: Pressure-Temp Pressure-Temp animated
Slide 23
If a sample of CO 2 had a pressure of 400torr at -7c, what
pressure would it have when heated to 60c? A. 329torr B. 500torr C.
-3429torr D. no change
Slide 24
This Law takes into account 3 variables by combining Charless
and Boyles laws. P 1 V 1 = P 2 V 2 T 1 T 2
Slide 25
A gas occupies a volume of 20 L at a pressure of 5 atm and a
temperature of 500K. What will the volume be if both the pressure
is raised to 10 atm and temperature is changed to 250K? rewrite to
put in the variables: A gas occupies a volume of 20 L (V1) at a
pressure of 5 atm (P1) and a temperature of 500K (T1). What will
the volume (V2) be if both the pressure is raised to 10 atm (P2)
and temperature is changed to 250K (T2)? Substituting into the
equation P1 V1 / T1 = P2 V2 / T2 we get: (5 atm ) (20 liter) / 500K
= (10 atm) ( V2) / 250K Solving for V2, (5 atm) (20 L) (250 K) / (
10 atm) (500 K) = V2 = 5 L
Slide 26
In order for a gas to lift off from the ground, it must have a
lower density that air. 2 ways to achieve low density 1. Choose a
gas with a low molar mass 2. Heat the gas
Slide 27
Diffusion is the mixing of gases in a system. Generally this is
from higher concentration to lower. Effusion is the escape of a gas
from a system molecule by molecule through a small hole, usually
between the molecules of the container.
Slide 28
The ideal gas law is the combination of Boyle, Charles, and
Avogadros law. It will take into account 4 variables: Pressure,
Temperature, Volume, and Moles. Ideal Gas: this is a gas that
follows the postulates of the kinetic theory. Most gases do this
unless under extreme pressure or extreme low temperature.
Slide 29
The ideal gas law is expressed as: PV=nRT P = pressure n= moles
V = volume T = temperature R = ideal gas law constant
Slide 30
R is the ideal gas law constant. The value of R is dependant on
the units of pressure and volume. The most common units used are
pressure in atm and volume in L. Therefore, the constant is.0821
atm*L/mol*K If pressure is in pa and volume in m 3 then 8.314 pa*m
3 /mol*K is used.
Slide 31
A sample of Iodine gas is put into a bottle at 60c and 1.4atm
of pressure. If the volume of the bottle is 500mL, how many grams
of iodine is there? P = 1.4atm V =.5L T= 333K R=.0821 n= ?
Questions to ask: What R will we use? What conversions do we need
to make 1 st. What do we need to find and then how do we get grams?
(1.4atm)(.5L) = (n)(.0821)(333K) (1.4atm)(.5L) = n (.0821)(333K) n
=.03mols I 2 For Grams:. 03mols I 2 x 254g I 2 = 7.62g I 2