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

H₂O is the excess reactant

It will fall off and tip over. 

The activity series is shown in the attached picture. if the element is below the other, then you can displace the other. following the activity series as a guide, the reactions are as follows: nickel and aluminum chloride3 ni + 2 alcl₃  → 3 nicl₂ + 2 albarium and copper bromideba + cubr  →  no reaction because cu is less oxidizable than bapotassium nitrate and aluminum3 kno₃ + al  → al(no₃)₃ + 3 ksodium phosphate and zincnaso₄ + zn  → znso₄ + na