Question

Two moles of magnesium (Mg) and five moles of oxygen (O2) are placed in a reaction vessel. When magnesium is ignited, it reacts with oxygen. What is the limiting reactant in this experiment?

Mg + O2 → MgO (unbalanced)

A.
Mg

B.
O2

C.
MgO

D.
both the reactants are in same proportion

Answer 1

`\boxed{\text{Mg is the limiting reactant}}`

Step-by-step explanation:

We are given the amounts of two reactants, so this is a limiting reactant problem.

We know that we will need moles, so, lets assemble the data in one place.

2Mg + O₂ ⟶ 2MgO

n/mol: 2 5

Calculate the moles of MgO we can obtain from each reactant.

From Mg:

The molar ratio of MgO:Mg is 2:2

`\text{Moles of MgO} = \text{2 mol Mg} * \frac{\text{2 mol MgO}}{\text{2 mol Mg}} = \text{2 mol MgO}`

From O₂:

The molar ratio of MgO:O₂ is 2:1.

`\text{Moles of MgO} = \text{5 mol O}_(2) * \frac{\text{2 mol MgO}}{\text{1 mol O}_(2)} = \text{10 mol MgO}\\\\\boxed{\textbf{Mg is the limiting reactant}} \text{ because it gives the smaller amount of MgO}`