The Chemistry in Airbags

Along with seat belts, air bags are one of the main mechanisms that reduce the risk of injury in the unfortunate case of a car accident. Once a car crashes, a sensor detects the strength of the collision and deploys an air bag by reacting three important chemicals, sodium azide (NaN₃) potassium nitrate (KNO₃), silicon dioxide (SiO₂). First, an electric impulse heats sodium azide to up to 300°C, causing it to decompose to nitrogen gas, which fills the airbag, and solid sodium, in the following redox reaction:

2 NaN3 -> 2 Na + 3N2

Since sodium metal is highly reactive, potassium nitrate first reacts to produce potassium oxide and sodium oxide and produce one more unit of nitrogen gas.

2Na + 2KNO3 -> 5Na2O + K2O + N2

Yet, the first period metal oxides are still quite reactive, so they are eliminated by silicon dioxide.

K2O + Na2O + 2SiO2 -> K2SiO3 + Na2SiO3

The end products, potassium silicate (K₂SiO₃) and silicate glass (Na₂SiO₃), are much more stable; nitrogen gas inflates the airbag and protects you from the collision.

 How do airbags protect you?

According to Newton's second law:

F= ma = m (dv/dt)

So, if dt increases due to the presence of an air bag, F decreases, reducing the force that is exerted on the body and thus making injuries or death less likely.