Identify which element is being oxidized and which is being reduced
Mg (s) + 2H2O (g) = Mg(OH)2 (s) + H2 (g)
Oxidation is the loss of electrons.
Reduction is the gain of electrons.
Which as gained; which has lost.
To identify which element is being oxidized and which one is being reduced in a reaction, we need to look at the changes in oxidation numbers for each element.
In the given reaction:
Mg (s) + 2H2O (g) → Mg(OH)2 (s) + H2 (g)
The oxidation number of magnesium (Mg) in Mg (s) is 0 because it is an elemental form. In Mg(OH)2, the oxidation number of magnesium is +2.
The oxidation number of hydrogen (H) in H2O is +1. In H2, the oxidation number of hydrogen is 0.
From the changes in oxidation numbers, we can see that the oxidation state of magnesium goes from 0 to +2, meaning it loses electrons and is oxidized. On the other hand, the oxidation state of hydrogen goes from +1 to 0, meaning it gains electrons and is reduced.
Therefore, in the given reaction, magnesium (Mg) is being oxidized, and hydrogen (H) is being reduced.