How many grams of magnesium oxide are formed if 20.9 grams of Mg and 15.2 g of O2 react.

Mass of magnesium oxide formed = 35.1 g

Explanation:

Given data:

Mass of Mg = 20.9 g

Mass of O₂ = 15.2 g

Mass of magnesium oxide formed = ?

Solution:

Chemical equation:

2Mg + O₂     →   2MgO

Number of moles of Mg:

Number of moles = mass/molar mass

Number of moles = 20.9 g/ 24 g/mol

Number of moles = 0.87 mol

Number of moles of O₂:

Number of moles = mass/molar mass

Number of moles = 15.2 g/ 32 g/mol

Number of moles = 0.475 mol

Now we will compare the moles of MgO with magnesium and oxygen.

                Mg          :         MgO

                  2           :           2

                0.87        :         0.87

                  O₂         :         MgO

                     1         :            2

                   0.475   :        2/1×0.475 = 0.95  

Number of moles of MgO formed by Mg are less thus Mg will limiting reactant.

Mass of MgO:

Mass = number of moles × molar mass

Mass = 0.87 mol × 40.3 g/mol

Mass = 35.1 g