Unit 2 Review : Gas Laws (Chapter 3 and 4)
Textbook Questions: page156: 1, 2, 3, 11, 13, 14 bc, 16, 17, 18, 19, 20, 21, 22, 25
Key Concept #1: Gas Properties and the Kinetic Molecular Theory
(text page 99)
• Properties of Gases
o compressible, low density, mix completely when in the same container, expand
when temperature increases
• Kinetic Molecular Theory
o particles of a gas are in constant motion
o travel in straight line until they collide with another particle or the wall of a
container
o collisions are perfectly elastic
o as temperature increases, kinetic energy increases
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Graphs:
Key Concept #2: Temperature and Pressure of Gases
Pressure
o is the force created when gas molecules collide with the wall of its container
• the more collisions there are with the wall of the container, the higher the
pressure (that is why decreasing the volume of a gas or increasing the
temperature will increase the pressure)
• Units of Pressure (memorize)
101.325 kPa = 760 torr = 760 mm Hg = 1 atm
Temperature
o a measure of the average kinetic energy of a gas
o as temperature increases, particle motion increases (particles move faster)
o Kelvin Temperature Scale: sets 0 K as the lowest possible temperature (the point
where molecular motion stops)
0 K = -273 ˚C
Key Concept #3: Boyle’s Law
(text page 109)
Boyle’s Law states that pressure is inversely proportional to volume for a given mass of
gas at a constant temperature (as one increases the other decreases)
Formula: P1V1 = P2V2
Example:
The volume of 400 mL of chlorine gas at 400 mm
Hg is decreased to 200 mL at constant
temperature. What is the new gas pressure?
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Key Concept #4: Charles’s Law
(text page 117)
Charles’s Law states that the volume of a fixed amount of gas at a constant pressure is
directly proportional to the temperature (as temperature increases so does volume)
Formula
temperature must be in Kelvin
Graph:
A party balloon containing 3.5 L of air is taken from inside a
house at 22 °C to the outdoors where the temperature is
-15 °C. The new volume of the balloon is ________ L.
Key Concept #5: Combined Gas Law
(text page 128)
(temperature must be in Kelvin, units of pressure and volume must be the same on both sides of
the equation)
A Chinook is a warm, dry winter wind that causes a rapid change in the weather in southern
Alberta. The final volume of a cubic metre (1.00 kL) of air at -23 °C and 102 kPa when the
conditions change to 12 °C and 96 kPa is predicted to be ________ kL.
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Key Concept #6: Avogadro’s Law
(text page 133)
equal volumes of all ideal gases at the same temperature and pressure contain the same
number of molecules
this allows us to calculate the molar volume of a gas (the volume that one mole of a gas
occupies at a given T and P)
SATP (100 kPa and 298 K)
v = 24.8 L/mol
STP (101.325 kPa and 273 K) v = 22.4 L/mol
V = nv
V = volume (L)
n = number of moles
v = molar volume (L/mol)
Key Concept #7: Ideal Gas Law
(text page 139)
PV = nRT
P = pressure in kPa
V = volume in L
n = moles
T = temperature in K
R = ideal gas constant (8.314 L•kPa/mol•K)
Large quantities of chlorine gas are produced from salt to make bleach and treat water. What is
the mass of chlorine in 170 L of gas at 35 °C and 400 kPa ?
Key Concept #8: Ideal verses Real Gases (text page 147)
• an ideal gas obeys gas laws over all temperatures and pressures (i.e. never condense
into a liquid)
• real gases obey gas laws over some temperatures and pressures
• the types of gases that follow the gas laws most closely have low intermolecular forces
(London, dipole and H-bonds)
o have low molecular masses
o are non-polar
• gases obey the gas laws most closely under conditions of
o low pressure
o high temperature
Things to Memorize
P 1V 1 = P 2V 2
V = nv
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SATP (100 kPa and 298 K)
v = 24.8
L/mol
STP (101.325 kPa and 273 K) v = 22.4
L/mol
101.325 kPa = 760 torr = 760 mm Hg = 1 atm
PV = nRT
0 K = -273 ˚C