Stuck on a chemistry problem! Please help??

[AC(:]

Hydrogen azide, HN3, decomposes on heating by the following balanced reaction:

 

2HN3(g) ---> 3N2(g) + H2(g)

 

If 3.0 atm of pure NH3(g) is decomposed initially, what is the final total pressure in the reaction container? What are the partial pressures of nitrogen and hydrogen gas? Assume the volume and temperature of the reaction container are constant.

 

 

I actually balanced the reaction and put that up there but now I'm stuck!

The answers:

Total pressure = 6.0 atm

Pressure of N2 = 1.5 atm

Pressure of H2 = 4.5 atm

 

I need EXPLANATIONS on how to get these answers. Please help!

[Mr Skeptic]

First, note that your equation starts with 2 molecules of H2N3, so either divide the whole equation by 2 or your final answers will be double (you can divide later if you prefer). In any case, gas pressure is related to the number of gas molecules rather than their composition -- a big gas molecule is pretty much equivalent to a small one. So all you have to do is consider how many molecules you end up with compared to how many you started with.

[CaptainPanic]

In short, you go from 2 molecules to 4 molecules.

 

Pressure is, in fact, just the amount of molecules per volume (regardless of the type of molecules!)... so if the amount of molecules doubles, then...