Question

Using your favorite search engine on the Internet, find what are the real chemical reactions that take place in commercial air bags. If the hits on the web refer you to some scientific journals or books, find these references in Canisius library. Based of the information that you find (1) write the balanced chemical reactions and calculate the amounts of substances that are needed to inflate the 70L commercial air bag. (2) discuss the environmental impact of used and unused air bags. resufi gstores a Sp

Answer 1

There are three reactions involved so the final product is harmless. The first step begins with the thermal decomposition of sodium azide, a explosive.

2NaN32Na+3N2

10Na2KNO3K205N a0N2

K2ONa0SiO2alkaline silicate

At the end you obtain a safe product, a glass (alkaline silicate), that is stable and unignitable.

First we need to calculate the number of moles of N₂ in 70L, this can be done with the ideal gas equation:

ΡγEnικι

Isolating n we have:

PV n = RT

At 1 atm and 273.15 K (standard conditions) we have

(latm) (70L) PV 3.12mol n= (0.082L * atm /mol * К) (273.15К)) RT

From the first equation, we obtain 3 mol of N₂ (from the thermal decomposition of 2 mol of NaN3 ), but there are also produced 2 moles of Na that react to form N₂ , we need to know how many moles of N₂ are produced in this second reaction , this is done as follows bearing in mind that we began with 2 moles of NaN₃:

1molN20.2molN2 2molNa (2molNaNs2molNaN10molNa

The total number of moles of produced nitrogen is:

N2total) nfir st +nsecond 3mol +0.2mol=3.2mol

So, for each 2 mol of NaN₃ are produced, in total, 3.2 mol of N₂. This is approximately the calculated amount so, you need 2 mol of NaN_3. Using the molar mass of the compound you get:

(2molNaN.)65gNaNs130gNaN3 molNaNs

You need approximately 130g of sodium azide for a 70L bag