# air bag inflation question?

Automobile air bags inflate following a serious impact. The impact triggers the following chemical reaction.

2NaN3(s) --> 2Na(s) + 3N2(g)

If an automobile air bag has a volume of 11.6 L, what mass of NaN3 (in g) is required to fully inflate the air bag upon impact? Assume STP conditions.

Anyone have any clue how to do this?

• 2 moles of sodium azide release 3 moles of N2 gas. Under STP conditions, 1 mole of gas has a volume of 22.41 L. To find out how many moles of N2 will be required to fill a volume of 11.6 L, divide.

11.6/22.41 = 0.518 moles N2 gas.

To find how many moles of sodium azide are needed to produce this amount, divide by 3 and multiply by 2 (2 NaN3 ≡ 3 N2)

0.518 mol N2 ≡ 0.345 mol NaN3

Sodium azide has a molar mass of 65.01 grams. 0.345 moles NaN3 will have a mass of 0.345×65.01 = 22.248 grams.

Therefore, to inflate an 11.6 L airbag, 22.248 grams NaN3 must be decomposed.

• Pity it wasn't 11.2 litres!!

1mol gas at STP = 22.4 litres

You want 11.6 litres = 11.6/22.4 = 0.5179 moles N2

2mol NaN3 produce 3 mol N2

2/3*0.5179 = 0.3453 mol NaN3 required

Molar mass NaN3 = 22.99 + (14.007*3) = 65.011g/mol

0.3453mol = 65.011*0.3453 = 22.45 grams.