1. Write the balanced chemical equation:

N₂ (g) + 3H₂ (g) → 2NH₃ (g)

2. Determine the mole ratio:

The balanced equation tells us that 1 mole of N₂ reacts to produce 2 moles of NH₃.

3. Convert grams of NH₃ to moles:

* Find the molar mass of NH₃: (14.01 g/mol N) + (3 * 1.01 g/mol H) = 17.04 g/mol

* Divide the mass of NH₃ by its molar mass: 1.7 g NH₃ / 17.04 g/mol = 0.1 mol NH₃

4. Calculate moles of N₂:

* Use the mole ratio from the balanced equation: (0.1 mol NH₃) * (1 mol N₂ / 2 mol NH₃) = 0.05 mol N₂

5. Convert moles of N₂ to grams:

* Find the molar mass of N₂: 2 * 14.01 g/mol = 28.02 g/mol

* Multiply moles of N₂ by its molar mass: 0.05 mol N₂ * 28.02 g/mol = 1.4 g N₂

Therefore, 1.4 grams of N₂ must react to form 1.7 grams of NH₃.