1. Intro—Airbags

2. How do airbags work in your car?
There is a Nylon bag inside your steering wheel
That bag contains solid sodium azide (NaN3) which is ignited with electricity when a crash sets off a trigger
2 NaN3 (s)  2 Na (s) + 3 N2 (g)
The nitrogen gas created in this reaction then fills the airbag!!
How Does An Airbag Work??? Watch this!

3. Problems with this reaction?
It produces sodium metal, which reacts with water to form hydrogen gas & it also produces enough heat to ignite the hydrogen gas
The reaction produces heat, so the gas is very hot inside of the airbag
NaN3 is very toxic
What Solutions did we see in the video???

4. 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 and easier to store before needed
The amount of dangerous chemical is minimal
Heat from the reaction is absorbed, in part, by the physical components of the airbag system (nylon bag, steering wheel etc.)

5. Section 3.1—States of Matter

6. Solids: Particles are closely packed together
Particles vibrate in place – in fixed positions
Particles can’t switch places
Have a definite shape
Have a definite volume

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

8. Gas Particles very spread out – they can be poured
Rapid, random motion
Highly compressible
No definite volume—they will fill container
No definite shape—take shape of container

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

10. Solid, Liquid or Gas? It depends on temperature.

11. Temperature of state changes
Freezing point = melting pint
Boiling point = condensation point
Example: Water will freeze or melt at 0°C – it just depends upon the direction of heat flow. If we are adding heat at 0°C then it will melt. If we take away heat at 0°C it will freeze! 

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

13. Section 3.2—Properties of Matter

14. Physical versus Chemical Properties
Physical Property
Chemical Property
Can be observed or tested without changing the arrangement of the atoms or molecules
When observed the atoms or molecules are changed into different substance(s)

15. Intensive and Extensive Properties
Intensive Property
Extensive Property
Size of the sample doesn’t matter.
Example: Water boils at 100°C at 1 atm no matter how much you have.
Size of the sample does matter
Examples: length

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

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

18. Are the following properties intensive or extensive?
Let’s Practice
Mass
Volume
Color
Flammability
Density
Example:
Are the following properties intensive or extensive?

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

20. DEFINITIONS – WHAT IS DENSITY
Density- the ratio of mass to volume of a sample
How heavy is it for its size?
Lead = high density…small size (volume) is very heavy (mass)
Air = low density…a large volume of gas has very little mass

21. DENSITY – HOW DO WE CALCULATE DENSITY?
In g/L or g/mL or g/cm3
Mass
In grams (g)
D = m V
Volume
In liters (L) or mL or cm3
Don’t try to cancel out the units…density has “2 units” – a mass unit over a volume unit!

22. EXAMPLE 1—SOLVING FOR DENSITY
What is the density of a sample with a mass of 2.50 g and a volume of 1.7 mL?

23. EXAMPLE 1—SOLVING FOR DENSITY
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?

24. Graphing Density
If we make the y-axis mass and the x-axis volume then…
Then the slope equals Density!

25. BEYOND THE DATA…..
Let’s calculate the DENSITY – or slope of this graph!
Change in Y/Change in X
(100g-50g)/(20cm3 - 10cm3)
50g/10cm3 = 5g/cm3
HOW can we determine the mass of this sample from the graph if we know the volume is 40cm3 ?
WE EXTRAPOLATE!! We follow the trend of the graph to predict data we did not gather! The Answer is……
200 grams!!!

26. Floating
Objects float when they are less dense than the substance they are in!
Fewer particles in the same space = less dense
More particles in the same space = More dense

27. If a 22.7 g sample has a volume of 47.8 mL, will it float in water?
LET’S PRACTICE 1
Example:
If a 22.7 g sample has a volume of 47.8 mL, will it float in water?

28. If a 22.7 g sample has a volume of 47.8 mL, will it float in water?
LET’S PRACTICE 1
m = 22.7 g
V = 47.8 mL
D = ?
Example:
If a 22.7 g sample has a volume of 47.8 mL, will it float in water?
The density of water is 1 g/mL. This sample’s density is lower. It will float.