Balance the following equations;

b) Fe3O4(s) + H2(g) ----> Fe(s) + H2O(l)


Fe3O4(s) + H2(g) ----> Fe(s) + H2O(l)

Since hydrogen and iron are elements we will balance them last, so only oxygen remains. How many oxygens on the left? I count 4. On the right? I count 1. To balance the oxygen atoms we place the coefficient 4 before water.

Fe3O4(s) + H2(g) ----> Fe(s) + 4H2O(l)

Now we can balance the iron and the hydrogen. There are 3 iron atoms on the right and 1 on the left. We need a coefficient of 3 for the iron on the right. Using the same logic for hydrogen we need a coefficient of 4 for hydrogen.

Fe3O4(s) + 4H2(g) ----> 3Fe(s) + 4H2O(l)

The equation is balanced.