Gas Laws, Explosions, and Air Bags

1  Gas Laws, Explosions, and Air Bags

Outline

2  Ideal Gas Law

PV = nRT

P = Pressure (in atmospheres)

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:

4  Why Use Moles ?

Water has the structure

H-O-H

and the formula H 2 O.

atomsdozens of atomsmoles of atoms
# H222
# O111

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.

2.0 g of hydrogen reacts with 16.0 g of oxygen to make 18.0 g of water

2.0 moles hydrogen atoms react 1.0 mole of oxygen atoms to make 1.0 mole of water.

2 H   +   1 O       1 H 2 O

6  Water to Steam

18.0 grams of water = 1 mole

7  Volume and Temperature

PV = nRT

Pressure and amount of gas constant

V T

If temperature increases, volume increases.

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

PV = nRT

Amount of gas and pressure held constant

PV = constant

If pressure increases, volume decreases.

10  Breathing

Inhale

Exhale

11  Pressure and Temperature

PV = nRT

Volume and amount of gas constant

P T

If temperature increases, pressure increases.

12  Tires, Pressure Cookers, and Coke

Heating a closed container increases the pressure of the gas inside the container.

13  Explosions

An explosion is due to rapid expansion of gas.

Expansion due to:

and/or

14  TNT

tnt.png


TNT is 2,4,6-trinitrotoluene

Reaction is:

2 C 7 H 5 N 3 O 6   +  10.5 O 2        14 CO 2   +  5 H 2 O  +  3 N 2

10.5 moles gas       22 moles gas

15  Air Bags

16  Airbag chemistry

Sodium azide (NaN 3 ) reacts to create sodium metal and N 2 gas.

Other chemicals added to 'neutralize' sodium

2 NaN 3        2 Na  +  3 N 2

10 Na  +  2 KNO 3        K 2 O  +  5 Na 2 O  +  N 2

K 2 O  +  Na 2 O  +  SiO 2        Na 2 K 2 SiO 4 (glass)

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

19  Safety Claims

National Safety Council

From 1990-2001

20  Risks

Area with 10 inches (25 cm) of air bag opening is 'danger zone'.

Individuals in most danger:




File translated from TEX by TTH, version 3.02.
On 25 Apr 2002, 07:59.