Question

Sodium azide (NaN3) is used in airbag of cars. This is safety device with inflates on an impact according to the reaction 2NaN3 → 2Na + 3N2

An air bag of a particular car can be filled with 44.8 L of gas at STP. The mass (g) of NaN3 required to fill this airbag completely at 298K and 1 atm. pressure is :

(A) 87

(B) 130

(C) 84

(D) 100

Answer 1

Correct answer is (A) 87

As the maximum volume of airbag will remain same irrespective of temperature hence to fill me bag at 298 K.

V = 44.8 L

T = 298 K

P = 1 atm

n (of N2) = 1.83

***** of NaN3 required = 2/3 x 1.83 = 1.22 mole

mass of NaN3 required = 1.22 × 65 = 79.4 g

⇒ So it should be bonus.

Comment : If we consider that airbag will contain same mole at both temperature (273 K & 298 K) (i.e. assuming volume expansion at bag with temperature)

So ***** of N2 at STP = 2 (T = 273 K)

***** of N2 at 298 K & 1 atm = 2

***** of NaN3 reqd. = 2/3 x 2 = 4/3

Mass of NaN3 required = 4/3 x 65 = 84 g.

So (A) can be considered with the above unjustified assumptions.