Question

When 4.0 mol H2O react with 4.0 mol Al in the reaction below, 2.7 mol of Al are used up in the reaction. How many moles of Al are left over unreacted?

2 Al + 3 H2O → Al2O3 + 3H2 (C?)


2.7 mol Al left over

2.0 mol Al left over

1.3 mol Al left over

0.7 mol Al left over

Answer 1

Answer : The moles of Al left over unreacted are, 1.3 mole

Explanation : Given,

The total moles of Al are taken in this reaction = 4.0 mole

The moles of Al used in this reaction = 2.7 mole

Now we have to calculate the moles of Al are left over unreacted.

The moles of Al are left over unreacted = The total moles are taken in this reaction - The moles of Al used in this reaction

The moles of Al are left over unreacted = 4.0 mole - 2.7 mole = 1.3 mole

Therefore, the moles of Al left over unreacted are, 1.3 mole

Answer 2

From the amounts given and the reaction, the limiting reactant would be H2O and the excess reactant would be Al. Only a part of the initial amount of Al is being used up in the reaction while all of the H2O is reacted. The amount of Al left unreacted is 4.0 mol - 2.7 mol = 1.3 mol Al. The correct answer is the third option.