Chapter 3: Airbags

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Chapter 3 Airbags
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Airbags

• This chapter will introduce the chemistry needed
  to understand how airbags work
• Section 3.1 States of matter Phase Diagrams
• Section 3.2 Properties Changes of matter
• Section 3.3 Density
• Section 3.4 Counting Molecules
• Section 3.5 Gas Behavior Gas Laws

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IntroAirbags

• http//youtu.be/dZfLOnXoVOQ

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How do airbags work in your car?

• Nylon bag inside your steering wheel
• Solid sodium azide (NaN3) with is ignited with
  electricity when a crash sets off the trigger
• 2 NaN3 (s) ? 2 Na (s) 3 N2 (g)
• The nitrogen gas fills the airbag

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Problems with this reaction?

• NaN3 is very toxic
• It produces sodium metal, which reacts with water
  to form hydrogen gas enough heat to ignite that
  hydrogen gas
• Reaction produces heat, so gas is very hot in
  airbag. An exothermic reaction.

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The FIX!

• Addition of potassium nitrate!
• It reacts with the sodium metal to form potassium
  oxide sodium oxide and nitrogen gas
• Following up with addition of silicon dioxide
  which reacts with the oxides to form silcates
  (glass).

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Why do we use it?

• It produces the gas very quickly,(at about 35 ms)
  4x faster than a blink of an eye
• Reactants are small to store before needed
• Amount of dangerous chemicals is minimal
• Heat from reaction is absorbed, in part, by the
  physical components of the airbag system

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Section 3.1
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Solid

• Closely packed
• strong attractive forces
• Vibrate in place low kinetic energy of particles
• Cant switch places
• Definite shape
• Definite volume
• Incompressible

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Liquid

• Particles more spread out than solid
• Weaker attractions
• Particles are free to move past each other flow
• Indefinite shape takes shape of container
• Definite volume
• Slightly compressible

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Gas

• Particles are very spread out
• weakest attractive forces
• Rapid, random motion High kinetic energy of
  particles
• Indefinite shapetake shape of container
• Indefinite volumethey will fill container
• Highly compressible

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Changes in State Endothermic

• Kinetic energy must be put INTO the substance in
  order to increase the motions of the molecules
  thus breaking the intermolecular forces holding
  the particles together.
• Melting change of state from a solid to a liquid
• Vaporization(Boiling or Evaporation) change of
  state from a liquid to a gas
• Sublimation change of state directly from a
  solid to a gas

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Physical Changes Names of the Phase Changes
Solid
Gas
Liquid
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Changes in State Exothermic

• Kinetic energy must be taken OUT of the substance
  in order for the molecules to slow down so the
  intermolecular forces can begin draw hold the
  particles closer together.
• Freezing change of state from a liquid to a
  solid
• Condensation change of state from a gas to a
  liquid
• Deposition change of state from a gas to a solid

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Changes in State
Endothermic
Exothermic
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Temperature of state changes

• Freezing point (fp) is the temperature at which a
  liquid turns into a solid
• Melting Point (mp) is the temperature at which a
  solid turns into a liquid
• freezing point is the same as melting point
• Example water has a melting point or freezing
  point of 0C

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Temperature of state changes

• Boiling point (bp) is the temperature at which a
  liquid turns into a gas
• Condensation Point (cp) is the temperature at
  which a gas turns into a liquid
• boiling point is the same as condensation point
• Example water has a boiling point or dew point
  of 100C

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Physical Property

• All substances have their own freezing and
  boiling points which make this property a great
  way to identify a unknown substance.

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Atmospheric Pressure vs Vapor Pressure
Pressure Atmospheric Pressure Vapor Pressure
Force per unit area created as gas molecules collide with objects Force per unit area exerted against a surface by the weight of the air molecules above the surface Force per unit area of the gas molecules above a liquid colliding
Usually measured in N/m2 but in chemistry we use atm or millimeters of mercury (mm Hg) The more air molecules above a surface, the more molecules to exert a force and thus higher air pressure The lower the attractive forces, the higher the vapor pressure
At sea level, atmospheric pressure equals 1 atm Substance with high vapor pressure are called volatile
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Temperature Controls Vapor Pressure

• Only 2 factors control the Vapor Pressure of a
  Liquid Nothing ELSE!!!!
• Temperature
• 2. Attractive forces of the liquid

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Vaporization Differences between Evaporation and
Boiling

• Evaporation occurs
• spontaneously at all temperatures
• at the surface of the liquid
• Boiling occurs
• when extra kinetic energy(heat) is added.
• at only 1 temperature dependent on pressure
• It takes place within the body of the liquid

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Real Definition of Boiling Point

• external atmospheric pressure vapor pressure
  of the liquid

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Real Definition of Boiling Point

• Since atmospheric pressure changes at various
  altitudes, normal boiling point is used to
  describe the temp at which a L?G at 1 atm or 760
  mmHg of pressure

29,000 Mount Everest
69.0
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Important Ideas

• The higher the
• altitude, the lower
• the atmospheric
• pressure!

• At higher altitudes, the boiling point is lower
• It takes longer to cook foods at higher altitudes
  (lower atmospheric pressures)

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Boiling Water By Changing Pressure

• http//www.kentchemistry.com/moviesfiles/Units/Gas
  Laws/vacuum.htm

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Heating Cooling Curves

• shows how solids, liquids gases change state
  when temperature is changed
• Plateaus the changes of state (freezing,
  melting, boiling condensation)
• Freezing Point Melting Point are at the same
  temperature or plateau
• Boiling Point Condensation Point are at the
  same temperature or plateau
• Slopes pure states (solid, liquid, gas)

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• At the plateaus, kinetic energy remains constant
  (temp. remains constant) while potential energy
  changes
• At the slopes, kinetic energy changes (temp.
  changes) while potential energy remains constant
• DANGER!!
• Notice that a gas
• can get higher
• than boiling point!

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Phase Changes
BP
100
KE is changing/PE in constant ?
0
FP
? KE is constant/PE in changing
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Heating Curve
Examples 1. What is the boiling point of the
substance? 2. What letter
represents the solid state only?
3. What letter represents the melting
process?
100C
A
B
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Cooling Curve
While the substance is cooling during the liquid
phase, the average kinetic energy of the
molecules of the substance a) decreases b)
increases c) remains the same
?
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Cooling Curve
Examples 1. What is the freezing point of this
substance?
70C
9 -2 7 min
2. How long does it take for
the gas to completely liquefy?
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Animation of Heating Curve

• http//www.kentchemistry.com/links/Matter/HeatingC
  urve.htm

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Phase Diagrams

• shows how solids, liquids gases change state as
  both temperature and pressure are changed
• Crossing a line between states determines the
  change state (boiling, melting, etc)
• A point directly on a line will identify the
  pressure and temperature (boiling point, melting
  point, etc.) of the change

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Important Points on Phase Diagram

• Triple Point is the temperature and pressure in
  which all 3 of the states coexist
• Critical Point is the temperature pressure at
  which a gas can no longer liquefy

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Phase Diagrams of Water Carbon Dioxide
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Phase Diagram of Water
?Temp. of line B at 1 atm (freezing point)
273 K ?Temp. of line C at 1 atm (boiling
point) 373K ?D is the triple point
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Phase Diagrams of Water
?E is the critical point ?What change of state
happens when you cross line B at a constant
pressure of 10 atm increasing temp?
melting ?What change of state occurs when you
cross line A at constant pressure of .001 atm?
sublimation ?What change of state happens when
you cross line C at 400 K to 300K at approx. 5
atm? condensation
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Section 3.2 What are the properties
changes occurring within the airbag?
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Physical versus Chemical Properties
Chemical Property
Physical Property
Characteristic that can only be determined or
measured as the substance changes into different
substances
Characteristic that can be determined or measured
without changing the substances identity
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Examples of Physical Properties

• COLOR ODOR
• TEXTURE BOILING POINT
• DENSITY SOLUBILITY
• VOLUME MASS
• HARDNESS
• MALLEABILITY /BRITTLENESS

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Physical Properties
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Examples of Chemical Properties

• BURNING/COMBUSTING
• RUSTING
• ROTTING
• FLAMMABILITY
• REACTIVITY
• NEUTRALIZATION
• DECOMPOSING

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Intensive and Extensive Properties
Extensive Property
Intensive Property
Size of the sample DOES NOT matter a big piece
a small piece are the same with respect to the
property
Size of the sample DOES matter a big piece a
small piece would be different with respect to
the property
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• Intensive
• Melting point/boiling point
• Density
• Color/Smell
• Conductivity
• Hardness

• Extensive
• Mass
• Volume
• Energy
• Length
• Shape

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SELF CHECK
Flammability Boiling point Solubility Malleability
Reactivity with oxygen
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Chemical Physical, Intensive Physical,
Intensive Physical, Intensive Chemical
Flammability Boiling point Solubility Malleability
Reactivity with oxygen
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Physical VS Chemical Changes
Physical Change the chemical structure of the
substances is not changed.
H2O(l)? H2O(g)
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Physical VS Chemical Changes
Chemical Change the chemical structures of the
substances are changed.
H2O(l)? H2(g) O2(g)
RECALL Another name for a chemical change is
called a CHEMICAL REACTION.
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Physical Chemical Changes

• Physical changes
• do not produce new
• substances
• breaking, dissolving, distilling, cutting,
• Changes in state (boiling, condensing, melting
  freezing)

• Chemical changes
• do produce new
• substances
• rusting, burning, metabolizing food, oxidation or
  reduction, reacting with oxygen, etc.

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Physical Chemical Changes
Alsoif a change can be un-done by a physical
change, then the original change was physical as
well.
If salt is dissolved in water, it seems to
disappear
many people think this is a chemical change.
But if the water is evaporated (a physical
change), the salt is left in the container.
Since the original change was un-done with a
physical change, then the original change (the
dissolving) was a physical change as well.
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Confusing changes
People often use the following terms incorrectly.

Definition
Term
Type of Change
Changes a solid into a liquid
Melting
Physical
Reacting with oxygen to produce CO2 and H2O
Burning
Chemical
Adding one substance to another to form a
homogeneous mixture
Dissolving
Physical
Heating a sample to evaporate the water
Drying
Physical
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RECALL the Possible Signs of Chemical Changes

• Gas production (bubbling)
• Energy change (getting hot or cold)
• Color change
• Light given off
• Formation of a precipitate (an insoluble
  substance formed from two soluble substances)

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Theyre Possible signs
Sometimes these signs accompany physical
changes as well!

• Gas production (bubbling). Bubbles are formed
  during boiling (a physical change)
• Energy change (getting hot or cold). Energy
  changes accompany changes in state (physical
  changes)
• Color change. Color change can occur due to
  dissolving a substance (a physical change)

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Section 3.3
Do you want high or low density in your airbag?
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Density
the ratio of mass to volume of a sample
How heavy is it for its size?
Lead high densitysmall size is very heavy Air
low densitylarge sample has very little mass
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Density
Mass In grams (g)
Density In g/L or g/mL
Volume In liters (L) or mL
Dont try to cancel out the unitsdensity has 2
units a mass unit over a volume unit!
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Floating
Objects float when they are less dense than the
substance they are in! Is vegatable oil
more or less dense than water?
Fewer particles in the same space less dense
More particles in the same space More dense
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Density Values the larger the value, the more
dense
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Density Varies with Temperature
WHY? Most substances will expand when heated,
increasing the volume decreasing the
density. Water is an exception As water is
cooled, it expands, increasing the volume
decreasing the density. Thus, ICE is less dense
than WATER!
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Calculating Volume using Water Displacement
The volume is the difference between the final
volume and the initial volume of water. What is
the volume of the dinosaur? ______________
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Example 1Solving for Density
Example What is the density of a sample with a
mass of 2.50 g and a volume of 1.7 mL?
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Example 1Solving for Density
D ? m 2.50 g V 1.7 mL
Example What is the density of a sample with a
mass of 2.50 g and a volume of 1.7 mL?
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Example 2Solving for Mass
Example What is the mass of a 2.34 mL sample
with a density of 2.78 g/mL?
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Example 2Solving for Mass
m ? V 2.34 mL D 2.78 g/mL
Example What is the mass of a 2.34 mL sample
with a density of 2.78 g/mL?
2.34 mL
2.34 mL
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Example 3Solving for Volume
Example A sample is 45.4 g and has a density of
0.87 g/mL. What is the volume?
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Example 3Solving for Volume
m 45.4 g D 0.87 g/mL V ?
Example A sample is 45.4 g and has a density of
0.87 g/mL. What is the volume?
V
V
0.87 g/mL
0.87 g/mL
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SELF CHECK
Example Is it aluminum? The metal has a mass of
612 g and a volume of 345 cm3.
The accepted density of aluminum is 2.70 g/cm3
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Graphing Density
If we make the y-axis mass and the x-axis volume
then
Then the slope equals Density!