Warm Up 4/9
Write the formula of magnesium
chloride.
Hint: Mg has a charge of +2. Cl
has a charge of -1.
Gas Laws
Lesson: Kinetic
Molecular
Theory
Solids/Liquids/Gases
Describe the molecules in the
following images.
Kinetic Molecular Theory
A model that assumes that an ideal
gas is composed of tiny particles
(molecules) in constant motion.
Ideal Gas- an imaginary gas that
perfectly fits all of the KMT.
5 Parts of KMT:
1. Matter is composed of very small
particles called molecules.
2. Molecules are in constant motion.
The collisions with the walls of the
container cause pressure.
Continued
3. When the molecules collide with
each other or the walls of a
container, there is no loss of energy
(elastic collision).
4. There are no forces of attraction
or repulsion between gas particles,
but they collide and change
direction.
5. The average kinetic energy of gas
particles depends on the temperature
of the gas.
Temperature- measure of the
average kinetic energy of
particles.
Draw a picture for each of
the parts of the KMT.
Lesson: Gas Laws
(Part 1)
Gas Laws
Gas laws express the
behaviors of gases as
mathematical relationships.
Boyle's Law
-Pressure and volume
-States that the pressure and volume of
a gas are inversely proportional to
each other at constant temperature.
Pressure Units
Standard atmosphere (atm)
1 atm= 760 mm Hg = 760 torr
Pascal- SI unit for measuring
pressure:
1 atm= 101300 Pa = 101.3 Kpa
Boyle's Law
Formula:
P1*V1 = P2*V2
P1= initial Pressure
P2= final pressure
V1= initial volume
V2= final volume
Boyle’s Law Example
A gas has a volume of 1.25 L and a
pressure of 755 torr. What will the
new volume be if the pressure is
increased to 2667.6 torr?
Charles' Law
-Volume and temperature
-The volume of a gas is directly
proportional to the temperature
at constant pressure.
Charles' Law
Formula:
V1
T1
=
V2
T2
V1= initial volume
V2= final volume
T1= initial temperature
T2= final temperature
**Temperature must be in Kelvin!
Charles’s Law Example 1
If a gas has a volume of 247 mL
at 25.0°C, what will the new
volume be if the temperature is
increased to 308°C?
Charles’s Law Example 2
If a gas has a volume of 247 mL
at 25.0°C, what will the new
temperature be if the volume is
increased to 255 mL?
Boyle’s
Practice Problems
1. A gas occupies 12.3 liters at a pressure of
40.0 mm Hg. What is the volume when the
pressure is increased to 60.0 mm Hg?
2. A gas occupies 11.2 liters at 0.860 atm. What
is the pressure if the volume rises to15.0 L?
Charles’
3. 600.0 mL of air is at 20.0°C. What is the
volume at 60.0 °C?
4. If 15.0 liters of neon at 25.0 °C is allowed
to expand to 45.0 liters, what will the new
temperature be?
Ideal Gas Law
Formula: PV = nRT
P= pressure
(in atm)
n = number of
moles
V = volume
(in Liters)
R = universal gas
constant (.0821)
T = temperature
(Kelvin)
Universal Gas Constant (R)
-value can vary depending on
pressure units being used.
R= 0.0821 L·atm
mol·K
Example #1 (Ideal Gas Law)
What is the pressure of 5 moles
of a gas at 30°C in a 2 liter
container?
P x 2 L = 5 mols x 0.0821 x 303 K
2L
2L
P = 60 atm
Example #2 (Ideal Gas Law)
A 250 mL of a gas exerts a pressure
of 760 torr at 10°C. How many
moles of gas are present?
1 atm x 0.250 L = n x 0.0821 x 283 K
(0.0821 x 283 K)
0.0821 x 283 K
n = 0.0108 mol
Lesson: Gas Laws
(Part 2)
Dalton's Law of Partial Pressures
-states that the pressure of a gas mixture is
the sum of the partial pressures of the
gases in the mixture..
Formula: Ptotal = P1+P2+P3+...
Example (Partial Pressure)
A mixture of oxygen, hydrogen and nitrogen
gases exerts a total pressure of 278 kPa. If the
partial pressures of the oxygen and the
hydrogen are 112 kPa and 101 kPa
respectively, what would be the partial
pressure exerted by the nitrogen?
278 – 112 – 101 = 65 kPa
Avogadro’s Law
-Volume and number of moles
-States that the volume and # of moles
of a gas are directly proportional to
each other at constant temperature
and pressure.
Avogadro’s Law
Also means: Equal volumes of 2
gases at the same temperature and
pressure have equal numbers of
moles.
STP = Standard Temperature and
Pressure (0°C, 1 atm)
1 mole of gas = 22.4 L at STP
Avogadro‘s Law
Formula:
V1= initial volume
V2= final volume
n1= initial # of moles
n2= final # of moles
Example
Moles: 0.214
Moles: 0.375
Volume: 652 mL Volume: ?
V2
652 mL
=
.214 mol .375 mol
652 x .375 / .214 = 1142 mL
Left Side Practice
1. If a mixture of oxygen gas and water vapor
have a total pressure of 754 torr, and the
water vapor has a partial pressure of 21 torr,
what is the partial pressure of the oxygen?
2. Moles: 9.6
Moles: 6.8
Volume: 100.0 L Volume: ?
3. If 2.00 mol of gas occupies 4.50L at STP.
How much of the same gas will occupy
3.00L at STP?
4. A propane tank containing 55L has 2.46
moles of the gas. (C3H8 is propane!)
What would be the number of moles if ½
of the gas is used?