Consider the reaction Mg2Si (s) 4H2O (l) -> 2Mg(OH)2 (aq) SiH4 (g). Which of the reactants is in excess if we start with 50.0 grams of each reactant

H₂O is the excess reactant

Explanation:

A reactant is in excess when the other reactant is over and the first reactant is still present.

For the reaction:

Mg₂Si (s) 4H₂O (l) → 2Mg(OH)₂(aq) + SiH₄ (g)

We need to convert mass of each reactant to moles in order to find which reactant is in excess as follows:

Moles Mg₂Si -Molar mass: 76.7g/mol-:

50.0g * (1mol / 76.7g) = 0.652 moles of Mg₂Si

Moles H₂O - Molar mass: 18.02g/mol-:

50.0g * (1mol / 18.02g) = 2.78 moles of H₂O

For a complete reaction of 2.78 moles of H₂O are required:

2.78mol H₂O * (1mol Mg₂Si / 4mol H₂O) = 0.694 moles Mg₂Si

As there are just 0.652 moles, Mg₂Si is limiting reactant and

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