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 — A, sodium azide into nitrogen gas. On impact, a sensor ignites sodium azide (NaN3), which decomposes almost instantly: 2 NaN3 -> 2 Na + 3 N2. The large volume of nitrogen gas produced in milliseconds inflates the airbag, cushioning the occupant.
- (b)Solid carbon dioxide into gaseous carbon dioxide — Sublimation of dry ice is a physical change, not the impact-triggered chemical reaction used in airbags; it is far too slow and uncontrolled for the purpose.
- (c)Carbon dioxide into carbon monoxide — This is not the airbag reaction, and it would reduce, not suddenly increase, the gas volume in a useful, safe way.
- (d)Sudden conversion of gaseous carbon dioxide into carbon monoxide — Not the airbag mechanism; airbags rely on the rapid decomposition of sodium azide to nitrogen, not on any CO2-to-CO conversion.
A vehicle airbag inflates because a solid propellant undergoes a very fast decomposition reaction that releases a large volume of gas. The classic system uses sodium azide (NaN3): a crash sensor triggers its ignition and it decomposes to sodium metal and nitrogen gas in about 30-50 milliseconds. Secondary reagents (e.g. potassium nitrate and silica) then safely convert the reactive sodium into harmless glass-like silicates.
The question describes 'a chemical reaction … producing a gaseous product that causes a sudden volume change'. Only sodium azide -> nitrogen fits: a genuine, extremely fast chemical decomposition that makes a big burst of gas. The dry-ice option is a physical change; the CO2/CO options are neither fast nor volume-increasing.
- Airbags inflate by the rapid decomposition of sodium azide: 2 NaN3 -> 2 Na + 3 N2.
- The reaction produces nitrogen gas in about 30-50 milliseconds.
- The reactive sodium is neutralised by additives into stable silicates.
- Sublimation of dry ice (option b) is a physical change, not this reaction.
- Choosing the dry-ice option — that is a physical change, not a chemical reaction.
- Assuming any CO2 reaction; airbags specifically use sodium azide.
Asked as the chemical reaction behind airbag inflation, testing decomposition reactions in daily life.
No directly related past PYQ was found.
- practice — not a real PYQ
The gas that inflates a car airbag is
- (a)oxygen
- (b)nitrogen
- (c)carbon dioxide
- (d)helium
Answer(b) nitrogen, from the decomposition of sodium azide.
- practice — not a real PYQ
The decomposition 2 NaN3 -> 2 Na + 3 N2 is an example of a
- (a)combination reaction
- (b)decomposition reaction
- (c)displacement reaction
- (d)neutralisation reaction
Answer(b) decomposition reaction.