Question

Data Table 3: 80-L Driver-Side Air Bag

Activity Calculations

Moles of CO2 required to inflate 80-L driver-side air bag at room temperature and pressure 3.25moles

Balanced equation for the reaction of NaHCO3 and CH3COOH NaHCO3+CHCOOH=CH3COONa+H2O+CO2

Grams of NaHCO3 needed for the reaction 273 g

mL of CH3COOH (0.833 M) needed for the reaction 3.9 L, 3900mL

Data Table 4: 160-L Front Passenger-Side Air Bag

Activity Calculations

Moles of CO2 required to inflate 160-L front passenger-side air bag at room temperature and pressure 7.14 moles

Balanced equation for the reaction of NaHCO3 and CH3COOH NaHCO3+CHCOOH=CH3COONa+H2O+CO2

Grams of NaHCO3 needed for the reaction 599.76, 600 grams

mL of CH3COOH (0.833 M) needed for the reaction 8.57L, 8470mL

Based upon the observed performance of the air bag models and the amounts of sodium bicarbonate and acetic acid (vinegar) needed for an automotive air bag of 80 or 160 L, are these reactants a good substitute for sodium azide? One additional note regarding sodium azide: the rate of inflation after a triggering impact is 40 milliseconds (0.04 s).

Answer 1

No, sodium bicarbonate and acetic acid reactants can not be the substitute for sodium azide. The following points can explian it:

Inflation of air bag by filling of N2 through decomposition reaction of sodium azide is like an explosion reaction and completes with in milli seconds while the reaction between sodium bicarbonate and acetic acid is not that fast.

Air bag should be filled with either inert or non harmful gas. Sodium azide fills the bag with Nitrogen which is an inert gas whose behavior can be approximated as an ideal gas at the temperature and pressure of the inflating airbag. But the reaction of Sodium bicarbonate and acetic acid produce Carbon dioxide which can be harmful during deflation of bag and is a reactive gas.

In the Sodium azide reaction we need to analyze only one reactant and there is no rate limiting substance therefore the reaction would be more efficient than the reaction involve two reactants.

Another point is Amount of sodium azide required to fill 60L bag at room temperature and pressure is:

The reaction is

From the ideal gas law

Moles of Nitrogen gas required to fill 80 L volume of bag:

to produce 4.256 moles of nitrogen , Moles of sodium azide required =

Weight of 2.837 moles sodium azide  

Similarly for 160L air bag we need sodium azide.

Therefore as compare to sodium bicarbonate and acetic acid very less amount of sodium azide is required for the reaction.

Last point it is very difficult to store around 9L of acid with 600g of sodium bicarbonate in air bag and to create an electric impulse to induce the reaction to perform at the time of crash. In case of sodium azide as it is in solid form and less amount needed for reaction it is easy for storage in car bag and is easy to ignite the reactant through simple eelectric impulse.