Gas Laws, Explosions, and Air Bags
1 Gas Laws, Explosions, and Air Bags
Outline
- Gas Laws
- Applications
- Hot Air balloons
- Explosions
- Air Bags
2 Ideal Gas Law
V = Volume (in liters)
n = Amount of gas present (in moles)
R = Gas Law Constant (0.082 [ L atm/mol K] )
T = Absolute temperature (in degrees Kelvin)
3 Mole
A 'mole' is a counting unit used for atoms, molecules, ...
Analogous to a six-pack (6), a dozen (12), or a ream (500)
A mole is NOT:
- Weight (how much does a dozen weigh?)
- Dependent on type of stuff (a dozen is 12)
4 Why Use Moles ?
Water has the structure
- Chemical reactions based on atoms, which are too small to measure.
| atoms | dozens of atoms | moles of atoms | |
| # H | 2 | 2 | 2 |
| # O | 1 | 1 | 1 |
5 Moles and Weight
We don't buy jellybeans, flour, gasoline, or countless other small items by 'each'.
We buy these by weight or volume.
Chemists use compounds by mass, then convert to moles to get ratios.
Ex.
6 Water to Steam
18.0 grams of water = 1 mole
- Liquid
- Volume » 18 mL (3-4 Tablespoons)
- Gas
- Volume = [ nRT/P] = [ (1mole)(0.082)(298 K)/(1 atm)] = 22.4 Liters (about 5.5 gallons)
- (Assumes room temperature and 1 atmosphere pressure)
7 Volume and Temperature
- Given
- If
- Then
8 Hot Air balloons
Assume a balloon has a volume of is 300,000 L and the temperature is room temperature.
If the average temperature is increased 50 C 0 , then the volume of gas should increase to about 350,000L.
Since the volume of the balloon is roughly fixed, about 50,000 L of air is 'lost'.
50,000 L of air weighs » 50 kg
9 Pressure and Volume
- Given
- If
- Then
10 Breathing
Inhale
- Muscles pull lungs further open to increase volume.
- Pressure inside lungs decreases.
- Outside air enters to equalize pressure
- Muscle squeeze lungs to decrease volume
- Pressure inside lungs increases.
- Air leaves lungs to equalize pressure
11 Pressure and Temperature
- Given
- If
- Then
12 Tires, Pressure Cookers, and Coke
Heating a closed container increases the pressure of the gas inside the container.
- Friction of tires with road surface increases temperature of air in tires and increases the air pressure.
- In pressure cookers, higher pressure makes it more difficult for water to boil. Result is that water boils at a higher temperature.
- Pop left in car on hot summer day can 'explode'.
13 Explosions
An explosion is due to rapid expansion of gas.
Expansion due to:
- Increased temperature (reaction gives off heat)
- Creation of a gas (gas is product of chemical reaction)
14 TNT
|
15 Air Bags
- Scientific American - Chemistry of Air Bags
- Natl. Highway and Transportation Safety Assoc. - Air Bag Safety
- National Safety Council - Safety statistics
- Highway Safety Organization - Q & A regarding safety
- Victims of Airbag Syndrome - Claims that airbags release toxic chemicals
- Airbag on/off site - Promotes installation of airbag shutoff switches.
16 Airbag chemistry
Sodium azide (NaN 3 ) reacts to create sodium metal and N 2 gas.
Other chemicals added to 'neutralize' sodium
17 Sodium Azide
Very toxic compound. (More toxic than cyanide)
While some of this might escape during deployment, a more serious concern is what this chemical is doing in junkyards.
Recycling or controlled deployment would solve problem.
Currently unregulated.
18 Deployment Details
- Air bag volume is » 70 L
- Requires » 130 grams of sodium azide.
- Full deployment in approximately 0.03 seconds
- Velocity of airbag typically close to 200 mph during inflation
19 Safety Claims
- 175 deaths from airbags
- 3.3 million deployments
- 6377 lives saved
- ? injuries caused/prevented
20 Risks
Area with 10 inches (25 cm) of air bag opening is 'danger zone'.
- Arms, fingers, faces, ... in this area during deployment likely to be seriously injured.
- children
- shorter adult drivers (too close to steering wheel)
- any unrestrained individual (no seat beat)
File translated from TEX by TTH, version 3.02.
On 25 Apr 2002, 07:59.