Final answer:
To determine the mass of oxygen that reacts with 12g of magnesium, one must calculate the number of moles of magnesium present and then use stoichiometry based on the balanced chemical equation 2Mg + O2 → 2MgO to find the corresponding moles and mass of oxygen gas needed.
Step-by-step explanation:
Determining the Mass of Oxygen
To calculate the mass of oxygen that reacts with 12g of magnesium (Mg), we need to use stoichiometry, which is based on the balanced chemical equation for the reaction between magnesium and oxygen to form magnesium oxide (MgO).
The balanced chemical equation for the reaction is:
2Mg + O2 → 2MgO
This equation tells us that two moles of magnesium react with one mole of oxygen gas. First, we calculate the number of moles of magnesium present in 12g of Mg using the molar mass of Mg, which is 24.305 g/mol.
Moles of Mg = mass of Mg / molar mass of Mg
Moles of Mg = 12g / 24.305g/mol
Moles of Mg = 0.493 moles of Mg
According to the stoichiometry of the reaction, 2 moles of Mg react with 1 mole of O2, so 0.493 moles of Mg will react with half that amount of O2, which is 0.493 / 2 = 0.2465 moles of O2.
The molar mass of O2 is 32.00 g/mol (16.00 g/mol for each oxygen atom). Therefore, we can calculate the mass of O2 that will react with 0.493 moles of Mg:
Mass of O2 = moles of O2 × molar mass of O2
Mass of O2 = 0.2465 moles × 32.00 g/mol
Mass of O2 = 7.888 g of O2
7.888 g of oxygen gas is necessary to react completely with 12g of magnesium to yield magnesium oxide.