1.4 GASES
Useful websites:
Properties of Gases (Gas Laws)
http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/gasesv6.swf
Gas Laws (NASA)
http://www.grc.nasa.gov/WWW/K-12/airplane/Animation/frglab.html
Kinetic Molecular Theory
The Kinetic Molecular Theory states that:
1) Particles are in _________________ motion and…
2) The extent of particle motion depends on the absolute __________________ (i.e. the Kelvin
temperature)
Simply put, _______________________ zero [O K(elvin) or -273.15 °C] means there is ______ particle
motion – all ____________________(straight-line), ___________________, and _________________
motion _________. So you can’t go below absolute zero, because once motion is stopped, it can’t be
more stopped!
Temperature is therefore a measure of ________________ energy or _____________ of the particles.
Greater temperature means that the particles have __________________ kinetic energy. The absolute
temperature scale is measured in ______________. Zero Kelvin means __________ kinetic energy.
*Throughout this unit, make sure all temperatures are expressed in ____________________! (The
negative numbers used in other temperature scales mess up the calculations...)
*The Kelvin Temperature Scale
Convert the following to °C.
Absolute Zero =
Converting:
; 273 K =
; 298 K =
; 373 K =
K = °C + 273
(*Note the absence of the “degree” symbol when expressing temperature in Kelvin…do not say
“degrees” Kelvin…just “Kelvin”.)
Pressure
Pressure  the force per unit _____________ that the particles exert through _______________ with
the container ____________
Pressure can be measured in many different ways, all of which have some historical basis. However, two
common pressure units used in Chemistry are _______________ (kPa) and __________________ (atm).
 1 atm = ________________ kPa
 1 bar = _________________ kPa
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The GAS LAWS
1. Boyle’s Law (
Gas Law)
Boyle’s Law animation #1: http://www.grc.nasa.gov/WWW/K-12/airplane/boyle.html
Boyle’s Law animation #2:
http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/flashfiles/gaslaw/boyles_law_
graph.swf
Boyle’s Law is the relationship between _________________ and ______________. Pressure and
volume are ___________________ proportional. As the volume decreases, the particles are forced
closer together and so, the number of collisions with the sides of the container _______________, and
thus pressure increases. **Remember, this relationship only holds true for a _____________(constant)
_______________ of gas at a CONSTANT _____________________.
2. Gay-Lussac’s Law (
Law)
- Gay-Lussac’s Law Animation
http://www.juntadeandalucia.es/averroes/recursos_informaticos/andared02/leyes_gases/flash/l_gaylussac6cs.swf
Gay-Lussac’s Law is the relationship between ___________________ and ____________________. As
temperature increases, the kinetic energy of the particles _________________, therefore they are
colliding with the sides of the container with greater ____________________ and _______________.
Both of these factors cause the pressure to _______________. Pressure is __________________ to
temperature (see graph). *If the particles have zero kinetic energy, they can’t collide with the container
walls. **Remember, this relationship only holds true for a ________________ (constant) ___________
of gas at a CONSTANT __________________.
3. Charles’ Law (
Law)
Charles’ Law animation #1: http://www.grc.nasa.gov/WWW/K-12/airplane/glussac.html
Charles’ Law animation #2: http://www.chem.ufl.edu/~itl/2045/greenbowe_sims/charles_law.swf
Charles’ Law is the relationship between ___________________ and __________________. As
temperature increases, so does the kinetic energy of the particles. This causes them to collide more
______________________ and with more _____________, and therefore _____________ out. Volume
is _____________________ to temperature (see graph). **Remember, this relationship only holds true
for a FIXED (constant) MASS of gas at a CONSTANT ______________________.
4. The Combined Gas Law
(…a combination of Laws 1, 2 & 3 ; applies ONLY TO A _________________ AMOUNT OF GAS)
Q. How will the volume of an ideal gas change when the pressure is quadrupled and the absolute
temperature is tripled?
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5. Avogadro’s Law [
(of gas)-
Law]
Up until now, we have been concerned only with a FIXED amount (or mass) of gas. Now we consider
how changing the number of __________________ (amount) of gas affects its __________________.
Avogadro’s Law is the relationship between number of ________________ (i.e. moles of gas) and the
__________________ the gas occupies.
Avogadro’s Law defined: Avogadro’s Law states that ___________________ VOLUMES OF _______ GAS
(at the same ______________________ and ____________________) contain an __________ NUMBER
OF MOLES of GAS. Or, put another way…the VOLUME occupied by a gas is ____________________ to
the NUMBER OF ____________ of gas present at constant pressure and temperature.
Avogadro’s Law of Combining Volumes
As a result of Avogadro’s Law, the mole ratios given in a balanced chemical equation, involving
EXCLUSIVELY _____________, can be treated as __________________ ratios also.
Consider the following example: (Assume the reaction goes to completion.)
The Reaction
N2(g)
+
3H2(g)

2NH3(g)
Mole Ratios
Volume(L)Ratios
1 mole of N2 + 3 moles of H2 react to produce 2 moles of NH3
1 Litre of N2 + 3 Litres of H2 react to produce 2 Litres of NH3
Q. What volume of ammonia will be produced by the reaction of 4.0 L of N2 and 9.0 L of H2?
Standard Molar Volume
Standard molar volume is the volume occupied by _________ MOLE of ________ GAS at standard
temperature and pressure (i.e. STP). The standard molar volume of any gas at STP is ________ L.
*STP
(Standard Temperature and Pressure)
Temperature = 273 K (0°C)
*SATP
(Standard Ambient Temperature and Pressure)
Temperature = 298 K (25°C)
Pressure = 100 kPa = 1 bar
Pressure = 100 kPa
Molar Volume = 22.7 L/mol = 22.7 dm3 mol-1
Molar Volume = 24.0 L/mol
*Values corresponding with IB Data Booklet
Practice Problems:
*Use proportions to solve the following:
1. A balloon contains 2.0 L of helium gas at STP. How many moles of helium are present?
2. What is the volume, at STP, of 3.45 mol of chlorine?
**Try to come up with a 3-variable formula that you could use to answer 1 and 2. How would this
formula change if the gas was at SATP?
*3. A sample of 0.0412 g of gas has a volume of 35.4 mL at 1 bar and 273K. Determine the molar mass of
the gas.
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6. The Ideal Gas Law
Ideal Gas Law: http://cwx.prenhall.com/petrucci/chapter6/medialib/tutor/9749.swf
*An ideal gas is a gas that does NOT have any:
1. MOLECULAR ____________________ …so that the volume of a gas can go to zero
nor any
2. _______________________ FORCES...so that the gas never condenses to a liquid
*Most gases behave as Ideal Gases because the volume of the gas is usually so much bigger than the
volume of the actual molecules that it is negligible, and they are at a temperature far above the
boiling/condensation points that the IMF’s are insignificant.
*Gases exhibit “non-ideal” behavior when they are under high pressures, and low temperatures.
*The physical behaviour of all ideal gases is governed by the Ideal Gas Law equation:
PV =
Where: (You must make sure you pay attention to units!...due to the commonly used value of R.)
i) R = 8.314 kPa•L•mol-1•K-1
(alternate units or 8.314 J K-1 mol-1)
*R is known as the Universal Gas Constant.
ii) P = Pressure in ____________________(kPa)
iii) V = Volume in _____________(L)
iv) n = number of moles(mol)
v) T = temperature in ________________(K)
[1.000 kPa = 1000 Pa] ; [101.3 kPa = 1.000 atm]
[1.0 L = 1.0 dm3] ; [1.000 m3 = 1000 dm3 = 1000 L]
**Whenever you have been given information about gases, check to see if they are at Standard
conditions (i.e. 1 bar & 273 K). If it is, then you don’t need to use PV = nRT, you can simply use:
V = 22.7 L/mol. (i.e. If you need to determine the volume or number of moles present at STP, use
n=
VSTP
) *Remember, if the gases are at STP, you already know the temperature and pressure!
22.7
Practice Problems:
1. 4.00 dm3 of ammonia gas in a container holds 2.17 mol at 206 kPa. What is the temperature inside
the container?
2.
a) Calculate the volume of 3.03 g of hydrogen gas at a pressure of 1.50 atm and a temperature of -64 °C.
b) Calculate its volume at STP. (Try doing this 2 different ways…just to prove a point.)
*3. An unknown gas of mass 0.625 g occupies a volume of 35.1 mL at 25°C and 1 x 10 5 Pa. Calculate the
molar mass of the gas.
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