A-Level The mole and reacting-quantity calculations: worked solution

Question

Give the balanced chemical equations for Step 2, in which lithium metal combines with nitrogen to give lithium nitride, and for Step 3, in which lithium nitride reacts with water to regenerate lithium hydroxide and ammonia. Using these, work out the mole ratio of the lithium formed in Step 1 to the ammonia formed in Step 3.

Step 2 (Li + N2 -> Li3N): 6Li + N2 -> 2Li3N Step 3 (Li3N + water -> LiOH + NH3): Li3N + 3H2O -> 3LiOH + NH3 Tracing the moles: 6 mol Li give 2 mol Li3N (Step 2), and 2 mol Li3N give 2 mol NH3 (Step 3). Therefore 6 mol Li correspond to 2 mol NH3. Mole ratio Li : NH3 = 6 : 2 = 3 : 1.