When 8.0 moles of methanol are reacted with 9.0 moles of oxygen, how many moles of water vapor does the reaction produce?

12 moles of H₂O are formed in this combustion.

Explanation:

First of all, think the reaction:

2CH₃OH (l) + 3O₂ (g) → 2CO₂ (g) + 4H₂O (g)

Ratio in the reactants is 2:3, so 2 mol of methanol need 3 mol of oxygen to react. Then 8 mol of CH₃OH, will need (8.3) / 2 = 12 moles of O₂

We have 9 moles of O₂, so this is the limiting reactant.

3 mol of oxygen produce 4 mol of water

Then, 9 mol of oxygen will produce (9.4) / 3 = 12 moles