Question

In a collision of sufficient force, automobile air bags respond by electrically triggering the explosive decomposition of sodium azide (NaN₃) to its elements. A 54.8−g sample of sodium azide was decomposed, and the nitrogen gas generated was collected over water at 26°C. The total pressure was 756.6 mmHg. How many liters of dry N₂ were generated?

______  L N₂

Answer 1

The balances reaction of sodium azide decomposition is

2Na3N ---------6Na+3N2

2 mole of Na3N gives 6 moles of Na and 3 moles of N2

moles= mass/molar mass

molar masses: Na3N= 3*23+14= 83, moles of Na3N in 54.8 gm= 54.8/83= 0.66

0.66 moles of Na3N gives 3*0.66/2= 0.99 moles

from gas law equation, PV= nRT, n=0.99 moles of N2 , R=0.0821 L.atm/mole.K, T=26deg.c= 26+273= 299K

P= partial pressure of N2= total pressure- saturation pressure of water

Antoine equation for water gives saturation pressure of water at 26 deg.c

log psat(mm Hg)= 8.07131- 1730.63/(t+233.426)

at 26 deg.c, log psat = 8.07131- 1730.63/(26+233.426), Psat= 25.14 mm Hg

partial pressure of nitrogen = 756.6-25.14=731.46 mm Hg= 731.46/760 atm =0.962 atm

V= nRT/P= 0.99*0.0821*299/0.962 L=25.26 L