Which one of the following equations is the balanced chemical equation for the given reaction? Fe + H2O → Fe3O4 + H2
- A.Fe + 4H2O → Fe3O4 + H2
- B.3Fe + H2O → Fe3O4 + 2H2
- C.3Fe + 4H2O → Fe3O4 + 4H2
- D.3Fe + 4H2O → Fe3O4 + H2
Correct answer
Explanation
The correct answer is C, 3Fe + 4H2O → Fe3O4 + 4H2. Only this equation has the same number of iron, hydrogen and oxygen atoms on both sides.
Iron reacts with steam to form iron(II,III) oxide and hydrogen gas. To balance it, start with iron: Fe3O4 has three iron atoms, so put 3 before Fe. Next, oxygen: Fe3O4 has four oxygen atoms, so four water molecules are needed, giving 4H2O. Those four water molecules carry eight hydrogen atoms, which make four H2 molecules. Check: 3 Fe, 8 H and 4 O on the left; 3 Fe, 8 H and 4 O on the right. A balanced equation obeys the law of conservation of mass.
A is wrong: it has one iron atom on the left against three on the right, and 8 H against 2 H.
B is wrong: it has one oxygen atom on the left against four on the right.
D is wrong: iron and oxygen balance, but 8 hydrogen atoms on the left give only 2 on the right.
Exam tip: balance metals first, then oxygen, then hydrogen, and finally recount every atom on both sides.
Practice Questions
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