urgent chem help?

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 74.4 L at STP?
please explain

Answer 1

Start with 74.4L N2 gas. End with g NaN3. Multiply the 74.4L N2 by 1mol N2/22.4L N2. This is the molar volume of an ideal gas at STP. The L N2 cancel to give moles of N2 gas. Multiply by 2mol NaN3/3mol N2. This comes from the balanced equation. The mol N2 cancel to give the moles NaN3. Multiply by 65g NaN3/1mol NaN3. The mol NaN3 cancel, giving g NaN3, the mass. Atomic weights: Na=23, N=14.

Answer 2

First convert the 74.4L of gas to moles, so divide by 22.4L/mol.

This gives you 3.3214 moles of N2. The ratio of NaN3 is 2:3, so multiply by 2/3. This gives you 2.2143 mol NaN3. Multiply moles by the molar mass of the solid (65.02 is what I used, it has enough Sig. Figs.) giving you 143.97g.

Always convert to moles, at least that's what always do if I'm stuck. Usually once you have the moles the rest is number crunching.

One thing though, STP is freezing temp, so I guess no one is inside the car when the air bags go off.

Answer 3

Find the moles of N2 produced.

PV = nRT
Fromt STP you know P,T. From your book you know R and V is given. So,
n = PV/RT
From the reaction you know that 3 moles of N2 required 2 moles of NaN3.

3 moles N2 ===> 2 moles NaN3
n moles N2 ===> x moles NaN3

x = 2n/3 moles NaN3.

If you want the response in grams multiply by the molecular weight of NaN3.