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 airbag List characteristics that you’d want to avoid in an airbag

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

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

Intro—Airbags

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

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 particles Vibrate in place Can’t switch places Definite shape Definite volume

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

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

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

Temperature of state changes Freezing point = melting point Boiling 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 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)

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

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?

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?

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?

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?