In a collision of sufficient force, automobile air bags respond by electrically triggering the explosive decomposition of sodium azide (NaN3) to its elements. A 29.4−g sample of sodium azide was...

Question

decomposed, and the nitrogen gas generated was collected over water at 26°C. The total pressure was 733.8 mmHg. How many liters of dry N2 were generated?

I got 1158.62 L but it is wrong.

Answer 1

2NaN₃ ==> 2Na + 3N₂

Total pressure = 733.8 mm Hg

Vapor pressure of H₂O @ 26ºC = 25.2 mm Hg

Vapor pressure due to N₂ gas collected over water = 733.8 mm Hg - 25.2 mm Hg = 708.6 mm Hg

Converting this to atm we have 708.6 mm Hg x 1 atm/760 mm Hg = 0.932 atm = P

Converting this to liters of N₂, we use the Ideal gas law: PV = nRT

To find moles N₂, we use the stoichiometry of the balanced equation:

29.4 g NaN₃ x 1 mol / 65 g x 3 mol N₂ / 2 mol NaN₃ = 0.302 moles N₂ = n

R = gas constant = 0.0821 Latm/Kmol

T = temp in K = 26 + 273 = 299K

Solving for V, we have...

V = nRT/P = (0.302)(0.0821)(299) / 0.932

V = 7.95 L