[BookwormElena]

I know how to find limiting reagent problems when given to masses, but I am having difficulty trying to figure out how to find the limiting reagent when given volumes and two different coefficients. ex:
   2 N₂(g) + 3 O₂(g)  2 N₂O₃

The nitrogen gas has a volume of 4.2 L and the oxygen has a volume of 6.3 L.
   Therefore would you divide the L of oxygen by 3 to see if there is enough nitrogen? Or vice versa? Since you can't find moles by dividing by the molar mass I am at a loss.

Any explanation would be highly appreciated! =)

[Borek]

Do you know ideal gas equation? Do you know Avogadro's law? What volume does 1 mole of gas occupy at STP?

[BookwormElena]

Yes, the ideal gas equation is PV=nRT, and Avagadro's number is 6.022 x 10²³ molecules/atoms per element/compound. One mol of liquid occupies 22.4 L at STP, but I'm not sure what mol of gas would occupy. The problem is set in STP so no need for any conversions right?

[BookwormElena]

If I divide the 6.3L of O₂ by 2, and divide the 4.2L of N₂ by 2 also, I should have approximately 2 times more L of O₂ than N₂ right?

[josharoon]

One mol of liquid occupies 22.4 L at STP, but I'm not sure what mol of gas would occupy.

Its actually one mole of gas which occupies 22.4L at STP.

Now I'm not 100% on how to answer this question but here it goes,
If you know that one mole = 22.4L you can find the amount of moles of each gas:
4.2/22.4=0.18750 <-- (moles of N₂)
6.3/22.4=0.28125 <-- (moles of O₂)

So as we know the ratio in the equation is 2N:3O we will have to divide the moles by their ratio so its 1:1 hence giving us the restricting reagent.
0.18750/2=0.9375
0.28125/3=0.9375
Therefore given your amounts of each gas there shouldn't be any excess of either 

[Borek]

Avagadro's number is 6.022 x 10²³ molecules/atoms per element/compound.

Avogadro's law says something about number of molecules in identical volume of gases.

As you were already told, 22.4L is a volume of gas, not liquid.

[BookwormElena]

Yay! Thank you so much! That makes sense now. I was always tripped up on limiting reagent problems with high coefficients, but now I understand. Thank you!