Question

Automotive air bags inflate when a sample of sodium azide, NaN3, is very rapidly decomposed to form solid sodium and dinitrogen gas.

What concerns do you think automotive air bag designers considered when selecting this reaction for their product?

What would you have to consider in order to determine the appropriate amount of sodium azide to include in an automotive air bag?

Answer 1

A) 2NaN3(s) ----> 2Na(s) + 3N2(g) ...(1)

There are sensors in the front of the automobile that detect a collision. These sensors send an electric signal to the canister that contains the sodium azide and the electric signal detonates a small amount of an igniter compound. The heat from this ignition starts the decomposition of the sodium azide and the generation of nitrogen gas to fill the air bag. What is particularly amazing is that from the time the sensor detects the collision to the time the air bag is fully inflated is only 30 milliseconds, or 0.03 second. Some 50 milliseconds after an accident, the car's occupant hits the air bag and its deflation absorbs the forward-moving energy of the occupant.

(B) First determine the amount and pressure of gas(N2) required using ideal gas equation and kinetic theory of gases. Then, use the stoichiometry from reaction (1) to determine the amount of NaN3.