Question

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 H2O, what is the limiting reactant?

Answer 1

Hi,

Answer: H20

Explanation:

Balanced equation for the given chemical reaction:

Mg (s) + 2 H₂O (g) → Mg(OH)₂ (s) + H₂ (g)

In order to find the limiting reactant in the above chemical reaction, we need to first calculate the no. of moles of magnesium and water.

Mass of Mg = 16.2 g

Molecular mass of Mg = 24.3 g/mol

Mass of H₂O = 12.0 g

Molecular mass of H₂O = 18 g/mol

∴ No. of moles of Mg = $\frac{mass}{molecular mass}$ = $\frac{16.2}{24.3}$ = 0.666 moles  

And,

No. of moles of H₂O = $\frac{mass}{molecular mass}$  = $\frac{12.0}{18}$ = 0.666 moles

From the balanced equation we can see that,  

1 mole of Magnesium requires 2 moles of H₂O

∴ 0.666 moles of Magnesium will require = 0.666 * 2 = 1.333 moles of H₂O

So, we can clearly see that 0.666 moles of Mg require 1.333 moles of H2O, but we have only 0.666 moles of water.  

Thus, H₂O is the limiting reactant.

Hope this helped!!!