1. Chapter 3: Airbags

2. Introductory Activity
What makes an effective airbag?
List criteria necessary to consider an airbag effective.
List characteristics that would be good in an airbag
List characteristics that you’d want to avoid in an airbag

3. Airbags
This chapter will introduce the chemistry needed to understand how airbags work
Section 3.1: States of matter
Section 3.2: Properties of matter
Section 3.3: Density
Section 3.4: Changes in matter
Section 3.5: Gas Behavior
Section 3.6: Counting Molecules
Section 3.7: Gas Laws

4. Kinetic Molecular Theory
Airbags
Use different
Work because of changes
Changes
States of Matter
To produce
Which is a
Gas
With different
Properties
Properties explained by
One of which is
Kinetic Molecular Theory
Density
Gas Laws
Explanation for

5. Intro—Airbags

6. 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

7. Problems with this reaction?
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
NaN3 is very toxic

8. Why do we use it?
It produces the gas very quickly, but not so quick that it’s more of a hazard
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

9. Section 3.1—States of Matter

10. Solid Closely packed together particles Vibrate in place
Can’t switch places
Definite shape
Definite volume

11. Liquid Particles more spread out than solid
Particles are free to move past each other
Slightly compressible
Definite volume
No definite shape – take shape of container

12. Gas Particles very spread out Rapid, random motion Highly compressible
No definite volume—they will fill container
No definite shape—take shape of container

13. Changes in State Gas Increasing molecular motion (temperature) Liquid
Sublimation
Boiling or
Evaporating
Liquid
Melting
Deposition
Condensing
Solid
Freezing

14. Temperature of state changes
Freezing point = melting point
Boiling point = condensation point

15. What’s between the particles?
Nothing! There is absolutely nothing between the particles!

16. Section 3.2—Properties of Matter
What properties are useful or not useful in an airbag?

17. Physical versus Chemical Properties
Physical Property
Chemical Property
Can be observed or tested without changing the atoms or molecules
In the process of observing or testing, the atoms or molecules are changed into different substance(s)

18. Intensive and Extensive Properties
Intensive Property
Extensive Property
Size of the sample doesn’t matter—you’d say a big piece and a small piece were the same with respect to this property
Size of the sample does matter—a big piece and a small piece would be different with respect to this property

19. Are the following properties are physical or chemical?
Let’s Practice
Flammability
Boiling point
Solubility
Malleability
Reactivity with oxygen
Example:
Are the following properties are physical or chemical?

20. Are the following properties are physical or chemical?
Let’s Practice
Flammability
Boiling point
Solubility
Malleability
Reactivity with oxygen
Chemical
Physical
Example:
Are the following properties are physical or chemical?

21. Are the following properties are intensive or extensive?
Let’s Practice
Mass
Volume
Color
Flammability
Texture
Example:
Are the following properties are intensive or extensive?

22. Are the following properties are intensive or extensive?
Let’s Practice
Mass
Volume
Color
Flammability
Texture
Extensive
Intensive
Example:
Are the following properties are intensive or extensive?