Airbags work on the principle of a chemical reaction triggered by the impact producing a gaseous product that causes a sudden volume change. Which one among the following chemical conversions is responsible for this ?
- A.Sodium azide into nitrogen gas
- B.Solid carbon dioxide into gaseous carbon dioxide
- C.Carbon dioxide into carbon monoxide
- D.Sudden conversion of gaseous carbon dioxide into carbon monoxide
Correct answer
Explanation
The correct answer is A, Sodium azide into nitrogen gas. In a crash a sensor fires an igniter, and sodium azide breaks down almost instantly into sodium and a large volume of nitrogen gas that fills the bag.
The reaction, 2NaN3 giving 2Na and 3N2, is complete in about 30 milliseconds, faster than the blink of an eye. Nitrogen is chosen because it is harmless and does not burn. The sodium metal formed is dangerous, so other chemicals such as potassium nitrate and silica are added to turn it into a safe glassy solid. Many newer airbags use other gas generators, but sodium azide is the classic example.
B is wrong because dry ice turns into gas slowly and is not used in airbags. C is wrong because carbon monoxide is poisonous and this change needs special conditions, not an impact. D is wrong for the same reason; no airbag fills with carbon monoxide.
Exam tip: airbag means sodium azide giving nitrogen gas in a few milliseconds.
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