Catalyst
 Review your Mock AP exam score and complete the reflection
sheet
 Turn into bin when completed.
Overall Score Distribution
Period 5
Period 2
Where We Are At
90
80
We have made
huge gains, but
we have more
work to do!
Percent Passing
70
60
50
40
30
20
10
0
Hispanic
National Average
Period 2
Period 5
Class Goal
Score Distribution
70
60
50
Period 2
Period 5
National Average
Hispanics
40
30
20
10
0
1
2
3
4
5
Heel Spurs
How Painful Are Those Shoes?
Lecture 4.1 – Pressure and Gas Laws
Today’s Learning Targets
 LT 4.1 – I describe what the pressure of a gas indicates and I can
calculate the pressure of a given substance.
 LT 4.2 – I can discuss the four gas laws (Gay – Lussac, Charles,
Boyle, and Avogadro) and solve complex equations that integrate
one or more of these using calculations.
 LT 4.3 – Using the four gas laws, I can derive the Ideal Gas Law.
Additionally, I can solve and apply this equation to a wide variety
of situations (density, molar mass, etc.)
Gases
 Recall, gases are moving in constant random motion
 They fill the entire container that they are contained in.
Pressure
 Pressure is the force exerted over a
given area
kg m
 Force is measured in Newtons ( s2 ).
 Area is measured in m2
 Pressure is measured in 
Pascals (Pa)
 Other units of pressure include
atmospheres, mm Hg, torr, and bar
F
P
A
Atmospheric Pressure
 The atmosphere exerts a pressure on
all objects
 Gas molecules are constantly colliding
with our bodies, create the observed
pressure.
 Less gas molecules the higher you go
up in the atmosphere, therefore
atmospheric pressure drops
 At sea level atmospheric pressure is:
 100 kPa
 1 atm
 1 barr
 760 mm Hg
Converting Between Pressure Units
1 atm = 1.01325 bar
1 atm = 760 mm Hg
1 atm = 760 torr
1 atm = 100 kPa
Measuring Pressure
 Pressure is measured using a barometer
 At atmospheric pressure, a tube without any gas, open at one end
and immersed in mercury will have the mercury rise 760 mm.
Monometers
 The sample gas is placed at one
end of the tube filled with
mercury.
 The height is added to the
initial mercury reading to get
the pressure of the gas of
interest.
Class Example
 An open end manometer with
atmospheric pressure at 760.
mmHg, and the mercury level was
120. mm higher on the right side
than the left. What was the gas
pressure in atm?
Table Talk
 Open end manometer,
atmospheric pressure 755 mmHg,
Hg level 75 mm higher on the
right. What was the gas pressure in
torr?
Standard Temperature and Pressure
(STP)
 Many problems are run at standard
temperature and pressure.
 Standard Temperature = 273.15 K
or 0 oC
 Standard Pressure = 1 atm
Around the World
 Around the room, there are 8 questions.
 Answer all 8 questions and check your answers on the back side of
the sheet.
Boyle’s Law
 If we keep temperature constant, then volume and pressure
are inversely related. As one goes up the other goes down
 Therefore, we can describe this relationship as:
V

1
P
Boyle’s Law
Graph of Boyle’s Law
This is an inverse
relationship! As one
goes up the other goes
down!
Charles Law
 As you heat up gas molecules they move quicker and this causes
them to hit the sides of the container with greater frequency.
 If the container is capable of expanding,, then the volume will
increase as the temperature increases.
 Therefore, we can describe this relationship as:
V

T
Charles Law Graph
This is a
direct
relationship!
Gay – Lussac’s Law
 Gas molecules move quicker the more we heat them up and
increase the temperature.
 This means that they will be hitting the sides of the container
more often and the pressure will also increase as the temperature
increases.
 We describe this by:
P

T
Gay-Lussac’s Law
Gay-Lussac’s Law
Absolute Zero
This is an direct
relationship! As
one goes up the
other goes up!
Avogadro’s Law
 Recall that if you have 1 mole of any gas, then it occupies 22.4 L
 This means that
V n
Ideal Gas
 An ideal gas is a theoretical gas that is made of randomly moving
particles that do not interact
 Most real gases behave like ideal gases at atmospheric pressure and
0 oC.
Deriving the Ideal Gas Law
 We know:

V
V
V



1
P
T
n
The Ideal Gas Law
PV  nRT
P = Pressure
V = Volume
n = Moles
T = Temperature
R = Gas Constant = 0.08206

L atm
mol K
Class Example
 Calcium carbonate decomposes upon heating to CaO and CO2. A
sample of CaCO3 is decomposed, and the carbon dioxide is
collected in a 250 mL flask. After decomposition is complete, the
gas has a pressure of 1.3 atm at a temperature of 31 oC. How
many moles of CO2 gas were generated?
Table Talk
 Tennis balls are usually filled with either air or N2 gas to have a
pressure above atmospheric pressure to increase their bounce. If a
tennis ball has a volume of 144 cm3 and it contains 0.33 g of N2
gas, what is the pressure inside the ball at 24 oC? HINT – 1 mL =
1 cm3.
Ideal Gas Law and Density
 Density is calculated by:
m
d
V
 We also know that if we have moles and want grams, then we use
the molar mass to convert:
m
n
MW
 Therefore, we can calculate the density of our gas by:

n Molar Mass P Molar Mass
Density 


V
RT
Class Example
 What is the density of carbon tetrachloride vapor at 714 torr and
125 oC
Table Talk
 The mean molar mass of the atmosphere at the surface of Titan,
Saturn’s largest moon, is 28.6 g/mol. The surface temperature is
95 K, and the pressure is 1.6 atm. Assuming ideal behavior,
calculate the density of Titan’s atmosphere.
Molar Mass and Ideal Gas Law
 We can rearrange our density equation to calculate the molar mass
of a gas:
dRT
Molar Mass
P

Class Example
 Calculate the molar mass of a gas if 2.50 g occupies 0.875 L at
685 torr at 25 oC
Table Talk
 Calculate the molar mass of a vapor that has a density of 7.135
g/L at 12 oC and 743 torr
White Board Races
Question 1
 At what temperature does 16.3 g of nitrogen gas have a pressure
of 1.25 atm in a 25.0 L tank?
Question 2
 What mass of CO2 is needed to fill an 80.0 L tank to a pressure of
150.0 atm at 27.0°C?
Question 3
 Calculate the density of HCl at STP
Question 4
 10 L of an unknown gas has a mass of 10.8 grams at a temperature
of 310 K and 1.2 atm. What is the molar mass of this mass? What
is the identity of the gas?
Question 5
 A gas mixture of helium and argon has a density of 0.704 g/L.
What is the percent composition of the mixture by mass.
Closing Time
 Read 10.1 – 10.5 and answer essential questions on reading
guide
 Complete book questions: 10.2, 10.4, 10.5, 10.13, 10.21 (skip
e), 10.25, 10.33, 10.36, 10.38, 10.39, 10.53, and 10.54