Stoichiometey problem

Question

The balanced equation is 3H2 + N2 —> 2NH3

If you need to make 2.00g of the NH3, what would be the mass of the reactants needed? The reactants are H2 and N2

Answer 1

Hello,Shrini,

A quick answer to this would be simply that the mass of the reactants must also be 2 grams, according to the conservation of matter law. But I suspect what is wanted are the specific masses of the hydrogen and nitrogen.

2 grams of NH₃ should be converted into moles, by dividing the mass by the molar mass of NH₃. 2g/17g/mole = 0.118 moles NH₃.

Now we can find the number of moles needed for the H₂ and NH₃ by looking at the molar ratios of these molecules compared to the ammonia molecule (NH₃).

Molar ratios:

H₂/NH₃ is (3/2)

Once we know the moles of H₂, we can find the moles N₂ required:

N₂/H₂ is (1/3)

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Hydrogen is then (3/2)*(0.118 moles NH₃) = 0.1764 moles, or 0.3528 grams.

Nitrogen is (1/3)*(0.1764 moles H₂) = 0.0588 moles N₂, or 1.64772 grams

Add the grams of nitrogen and hydrogen and we get a total of 2 grams, as predicted by the conservation of mass law.

Bob