Question

Use the chemical reactions that occur in an air bag to explain the importance of stoichiometry.

Answer 1

There are three reactions involved in the air bag chemistry. The material used is a solid mixture of sodium azide and an oxidizer, such as ferric oxide.

First sodium azide undergoes decomposition to give sodium metal and pure nitrogen.

2 NaN₃ (s) 2 Na (s) + 3 N₂ (g)

Now the sodium metal produced is highly dangerously reactive which is reacted with an oxidizer, ferric oxide that produces sodium oxide, iron and energy. The energy created here is used to expand the nitrogen gas to fill the bag.

6 Na (s) + Fe₂O₃ (s) 3 Na₂O (s) + Fe (s) + Energy

The sodium oxide produced in this reaction is extremely corrosive. The water vapour and carbon dioxide present in the air react with the sodium oxide to make sodium bicarbonate which turns it less harmful.

Na₂O (s) + 2 CO₂ (g) + H₂O (g) 2 NaHCO₃ (s)

Stoichiometry: The mass of gas that is required to fill an air bag depends on the density of the gas and the gas density depends on the temperature of the gas.

Hence, here the gas that is required to inflate the air bag is nitrogen.

It is very much important to have a right amount of sodium azide that produces the nitrogen for a particular bag. But it is also important to maintain the right temperature to expand the nitrogen to expand the nitrogen to a right level in the air bag.