How many grams of nitrogen are needed to produce 100 grams of ammonia gas?

82.4 grams N₂ (g)

Explanation:

3H₂ (g) + N₂ (g) = > 2NH₃ (g)

Assume excess H₂ (g).

Convert gms NH₃ to moles, solve for moles of N₂ by rxn ratio then convert back to grams N₂ (g).

Moles NH₃ (g) = 100g/17g·mol⁻¹ = 5.882 mole NH₃ (g)

Production of 5.882 mole NH₃ (g) requires 1/2 (5.882) mole N₂ (g) = 2.9941 mole N₂ (g)

Grams N₂ (g) needed = 2.9941 mole N₂ (g) x 28 gms/mole = 82.4 gms N₂ (g).