Robert S. answered • 04/06/21

Patient PhD Chemist with 40 Years of R&D And Teaching

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 NH_{3} should be converted into moles, by dividing the mass by the molar mass of NH_{3}. 2g/17g/mole = 0.118 moles NH_{3}.

Now we can find the number of moles needed for the H_{2} and NH_{3} by looking at the molar ratios of these molecules compared to the ammonia molecule (NH_{3}).

Molar ratios:

H_{2}/NH_{3} is (3/2)

Once we know the moles of H_{2}, we can find the moles N_{2} required:

N_{2}/H_{2} is (1/3)

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

Nitrogen is (1/3)*(0.1764 moles H_{2}) = 0.0588 moles N_{2}, 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