Question

Why is magnesium oxide the likely product of combustion of magnesium in air rather than magnesium nitride?

Answer 1

Combustion of magnesium metal in air leads exclusively to `"magnesium oxide"`.

Explanation:

While `"magnesium nitride"` is a possibility, and may even be more thermodynamically favourable than `MgO`, there is a kinetic barrier to the formation of the nitride, i.e. cleavage of the strong `N-=N` bond.

Here is video of an experiment oxidizing magnesium forming magnesium oxide. The procedure calls for addition of water to remove any magnesium nitride (unlikely) and added heating to ensure full oxidation of the magnesium.

Nitride formation thus requires a prohibitively high activation energy, and reaction with oxygen is more facile.