[Isomer]

I even have the answer to this question and I STILL don't know how to do it!!!!


Assume that an inflated air bag contains 169 L of Nitrogen gas at 25 degrees celsius and 485 kPa. What mass of sodium azide is required to produce this amount of nitrogen?

Here is the formula I figured....

2 NaN3 solid ---------> 3 N2 gas + 2 Na solid + 43.5 kJ

Info I calculated..

molar heat of formation of sodium azide is.....+ 21.8 kJ
molar mass of sodium azide is........+ 65.02
molar mass of nitrogen gas is.......+ 28.02

The formulas I've been fiddling with ( ^ means delta)

q = mc^t and ^h = n^h (formation)

I've tried anything and everything to no avail!

The answer is 1.43 kg. I think the 485 kPa is useless informatiion. And that is all I know! I am the chump who is stumped!!!

[skyglow1]

You need to use the equation pV=nRT to find out the number of moles of N₂ first I'm pretty sure. That is where the pressure comes in.

[lemonoman]

Yup.  Sorry to say the two equations you were fiddling with..."q = mc^t and ^h = n^h (formation)", aren't the ones you want.

If you're wondering how to catch these kinds of questions...we look at what we're given

"169 L of Nitrogen gas" gives a volume, V
"at 25 degrees celsius" gives a temperature, T
"and 485 kPa" gives a pressure, P
"What mass of sodium azide" says we want a mass, m.  Mass is always related to the amount of something, which is a counted number...as in moles of nitrogen...# of moles is usually n

So we have V, T, P, and we need m (or n, since n is related to m)

Sounds like work for PV=nRT ... and voila!  Best of luck!

[skyglow1]

Remember to convert to SI units before putting your values into the pV=nRT equation

[Isomer]

Thanks. I figured it out!!