Chapter 3: Airbags

Introductory Activity

What makes an effective airbag?List criteria necessary to consider an

airbag effective. List characteristics that would be good in

an airbagList characteristics that you’d want to

avoid in an airbag

Airbags

This chapter will introduce the chemistry needed to understand how airbags workSection 3.1: States of matterSection 3.2: Properties of matterSection 3.3: DensitySection 3.4: Changes in matterSection 3.5: Gas BehaviorSection 3.6: Counting MoleculesSection 3.7: Gas Laws

Airbags

States of

Matter

States of

Matter

Use different

PropertiesProperties

ChangesChanges

Gas LawsGas LawsDensityDensity

Kinetic Molecular

Theory

Kinetic Molecular

Theory

With different

Work because of changes

One of which is

GasGas

Properties explained by

To produce

Explanation for

Which is a

Intro—Airbags

How do airbags work in your car?

Nylon bag inside your steering wheelSolid 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

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

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

Section 3.1—States of Matter

Solid

Closely packed together particlesVibrate in placeCan’t switch placesDefinite shapeDefinite volume

Liquid

Particles more spread out than solidParticles are free to move past each otherSlightly compressibleDefinite volumeNo definite shape – take shape of container

Gas

Particles very spread outRapid, random motionHighly compressibleNo definite volume—they will fill containerNo definite shape—take shape of container

Solid

Liquid

GasSublimation

Melting

Boiling or Evaporating

Condensing

Freezing

Deposition

Incr

easi

ng m

olec

ular

mot

ion

(tem

pera

ture

)

Changes in State

Temperature of state changes

Freezing point = melting pointBoiling point = condensation point

What’s between the particles?

?

Nothing! There is absolutely nothing between the particles!

Section 3.2—Properties of Matter

What properties are useful or not useful in an airbag?

Physical versus Chemical Properties

Chemical PropertyPhysical 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)

Intensive and Extensive Properties

Extensive PropertyIntensive 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

Let’s Practice

Example:Are the

following properties are

physical or chemical?

Flammability

Boiling point

Solubility

Malleability

Reactivity with oxygen

Let’s Practice

Chemical

Physical

Physical

Physical

Chemical

Flammability

Boiling point

Solubility

Malleability

Reactivity with oxygen

Example:Are the

following properties are

physical or chemical?

Let’s Practice

Example:Are the

following properties are intensive or extensive?

Mass

Volume

Color

Flammability

Texture

Let’s Practice

Extensive

Extensive

Intensive

Intensive

Intensive

Mass

Volume

Color

Flammability

Texture

Example:Are the

following properties are intensive or extensive?