Metallic magnesium reacts with steam to produce magnesium hydroxide and hydrogen gas. If 16.2 g of #Mg# are heated with 12.0 g of #H_2O#, what is the limiting reactant?

1 Answer
A08
Feb 11, 2016

Water.

Explanation:

Balanced equation of the reaction is
#Mg+2H_2O->Mg(OH)_2+H_2 uarr#

Molar masses of elements in reactants
Atomic mass of Magnesium: 24.3050
Atomic mass of Hydrogen: 1.00794
Atomic mass of Oxygen: 15.9994

Given
12 gm of Water #=12.0/(2xx1.00794+15.9994)approx# 0.6661 moles
And 16.2 g of Magnesium #=16.2/24.3050approx# 0.6665 moles

We observe from the equation that
#1 # mol of magnesium requires #2# mols of water.

We require #2xx0.6665=1.333# moles of water to completely consume given quantity of magnesium. We have only 0.6661 moles.
Therefore, water is the limiting reactant.

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