Question

Air bags are activated when a severe impact causes a steel ball to compress a spring and electrically ignite a detonator cap. This causes sodium azide (NaN3) to decompose explosively according to the following reaction.

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

What mass of NaN3(s) must be reacted in order to inflate an air bag to 76.5 L at STP?

Answer 1

find out the no of moles of NaN3 using following formula

PV = nRT formula

STP means P = 1 atm , T = 273K,

R = 0.0821 L atm/mol-K

n = no o fmoles, V is given 76.5 L

we need to calculate n

put all these values in the above equation

1 atm x 76.5 L = n x 0.0821 L-atm/mol-K x 273K

n = 76.5 L / 22.41

n = 3.413 moles

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

from this balanced equation moles of 2 moles of NaN3 required to produce 3 moles of N2

moles of NaN3 required = 2/3 x 3.413 = 2.3 moles

now we got the moles of NaN3

find out the mass using formula

no of moles = weight / molar mass

weight = moles of NaN3 x molar mass of NaN3

weight = 2.3 moles x 65 g/mole

= 147.9 grams