Question

As magnesium burns in oxygen to produce magnesium oxide, there is no change in mass. Explain.

Answer 1

• When magnesium burns in oxygen, it produces a white powder called magnesium oxide. burning of magnesium ribbon in the air is a chemical reaction.

2 Mg(s) + O₂ (g) $\to$ 2MgO (s)

Magnesium Oxygen Magnesium oxide

• As we know, a chemical reaction always follows the law of conservation of mass, that is mass neither created nor destroyed in a chemical reaction.
• For example, in the above reaction, mass of magnesium at reactant side 48u (Atomic mass of Mg is 24u) and mass of oxygen is 32u, hence the total mass at reactant side is 80u. The total mass of MgO at product side is also 80u.

Hence, we can say burning of magnesium in air doesn't leads to change in mass.