How many grams of n2 are required to make 75 grams of nh3?

2.138 I think

Explanation:

N2 + 3H2 -> 2NH3

This means that 3 moles of H2 gives 2 moles of NH3

Lets convert 12.12 g of NH3 into moles.

The molecular weight of NH3 is 17 g/mol

So 12.12 g is 0.713 moles

If 2 NH3 comes from 3 moles of H2

1 mole comes from 1.5 moles of H2

So 0.713 moles of NH3 comes from 1.5 x 0.713 moles of H2 =1.069 moles of H2

1 mole of H2 weights 2g

So 1.069 moles of H2 weighs 2.138 g

n2(g) + 3h2-> 2nh3(g)   this is the balanced equation

note the mole ratio between n2, h2 and nh3.   it is 1 : 3 : 2   this will be important.

moles n2 present = 28.0 g n2 x 1 mole n2/28 g = 1 mole n2 present

moles h2 present = 25.0 g h2 x 1 mole h2/2 g = 12.5 moles h2 present

based on mole ratio, n2 is limiting in this situation because there is more than enough h2 but not enough n2.

moles nh3 that can be produced = 1 mole n2 x 2 moles nh3/mole n2 = 2 moles nh3 can be produced

grams of nh3 that can be produced = 2 moles nh3 x 17 g/mole = 34 grams of nh3 can be produced

note:   the key to this problem is recognizing that n2 is limiting, and therefore limits how much nh3 can be produced.