[nokia8650]

Hi

Could anyone please help me with the problem below

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

The sodium formed reacts with potassium nitrate:

10Na + 2KNO3(s) -> K2O(s) + 5Na2O(s) + N2(g)

Calculate the total mass of the solid mixture needed to produce 60 dm3 of nitrogen at room temp and pressure.

I can obtain the number of moles of Nitrogen gas, but dont know how to work out how many of these moles will come from each of the equations.

Thanks

[Borek]

I can obtain the number of moles of Nitrogen gas, but dont know how to work out how many of these moles will come from each of the equations.

First reaction equation tells you (look at the stoichiometric coefficients) that 2 moles of NaN₃ give 3 moles of N₂. That means that 1 moles of NaN₃ give 1.5 moles of N₂ and so on. It also means that to make 3 moles of N₂ you need 2 moles NaN₃ and so on.

[nokia8650]

Hi

Thanks for the reply.  I understand this, however, how do I know how much of the N2 came from the first equation, and how much came from the second.  Using this, I can work out the number of moles of NaN3 and KNO3 respectively in order to find their masses.

[Borek]

You may start with a single reaction equation that covers whole process, it will be something like

NaN₃ + KNO₃ -> K₂O + Na₂O + N₂

(not balanced yet).

You may also think this way: 1 mole of NaN₃ gives 1.5 mole of N₂ and 1 mole of Na. This one mole of Na gives 0.1 mole of N₂. Thus 1 mole of NaN₃ gives 1.5+0.1 mole of N₂... It is all in the reaction equations

[nokia8650]

Thanks alot!  I combined the two equations, as you suggested, and managed to obtain the answer.