Question

6.5 moles of Al (aluminum) reacts with 7.2 moles of H2O (water). Which is the limiting reactant? Calculate the theoretical yield. Balance equation : 2Al + 3 H2O == Al2O3 + 3H2

Answer 1

1. The limiting reactant is H₂O.

2. The theoretical yield of Al₂O₃ = 978.8 g.

Step-by-step explanation:

1. Which is the limiting reactant?

• The balanced equation for the mentioned reaction is:

2Al + 3H₂O → Al₂O₃ + 3H₂,

It is clear that 2.0 moles of Al react with 3.0 moles of H₂O to produce 1.0 moles of Al₂O₃ and 3.0 mole of H₂.

• From stichiometry; Al reacts with H₂O with (2: 3) molar ratio.

∴ 4.8 mol of Al (the remaining 1.7 mol is in excess) reacts completely with 7.2 mol of H₂O with (2: 3) molar ratio.

• So,

the limiting reactant is H₂O and the excess reactant is Al.

2. Calculate the theoretical yield.

• To calculate the theoretical yield, we should get the no. of moles of produced Al₂O₃:

Using cross multiplication:

2.0 moles of Al produce → 1.0 moles of Al₂O₃.

4.8 moles of Al produce → ??? moles of Al₂O₃.

∴ The no. of moles of Al₂O₃ produced = (1.0 mol)(4.8 mol)/(2.0 mol) = 9.6 mol.

∴ The theoretical yield of Al₂O₃ = (no. of moles)(molar mass) = (9.6 mol)(101.96 g/mol) = 978.8 g.