Green Chemistry and the Ten Commandments

3CH 4 + Fe 2 O 3 → Fe + 3CO 2 + 6H 2 O (4.2.6)

That gives a total of 12 O atoms on the right, 6 each in 3 CO 2 and 6 H 2 O. Taking 4 times
Fe 2 O 3 gives 12 Os on the left:

3CH 4 + 4Fe 2 O 3 → Fe + 3CO 2 + 6H 2 O (4.2.7)

The only species remaining to be balanced is Fe, which can be balanced by putting 8 in
front of Fe on the right. The balanced equation is

3CH 4 + 4Fe 2 O 3 → 8Fe + 3CO 2 + 6H 2 O (4.2.8)

Checking the answer shows on both left and right 3 Cs, 8 Fes, 12 Hs, and 12 Os
demonstrating that the equation is in fact balanced.

Exercise: Balance the following:

1. Fe 2 O 3 + CO → Fe + CO 2


2. FeSO 4 + O 2 + H 2 O → Fe(OH) 3 + H 2 SO 4


3. C 2 H 2 + O 2 → CO 2 + H 2 O


4. Mg 3 N 2 + H 2 O → Mg(OH) 2 + NH 2


5. NaAlH 4 + H 2 O → H 2 + NaOH + Al(OH) 3


6. Zn(C 2 H 5 ) 2 + O 2 → ZnO + CO 2 + H 2 O

Answers: (1) Fe 2 O 3 + 3CO → 2Fe + 3CO 2 , (2) 4FeSO 4 + O 2 + 10H 2 O → 4Fe(OH) 3

+ 4H 2 SO 4 , (3) 2C 2 H 2 + 5O 2 → 4CO 2 + 2H 2 O, (4) Mg 3 N 2 + 6H 2 O → 3Mg(OH) 2

+ 2NH 3 (5) NaAlH 4 + 4H 2 O → 4H 2 + NaOH + Al(OH) 3 , (6) Zn(C 2 H 5 ) 2 + 7O 2 →

ZnO + 4CO 2 + 5H 2 O

4.3. Just Because You Can Write It Does Not Mean That It Will Happen

The fact that a balanced chemical equation can be written does not necessarily mean
that the chemical reaction that it represents will occur. As an example, it is known that a
number of metals will react with acid to release elemental hydrogen gas and produce a
metal salt. For example, if iron wire, Fe, is placed into a solution of sulfuric acid, H 2 SO 4 ,
H 2 gas is evolved,

Fe(s) + H 2 SO 4 (aq) → H 2 (g) + FeSO 4 (aq) (4.3.1)

84 Green Chemistry, 2nd ed