Balancing Chemical Equations

Balancing Chemical Equations

The key in balancing chemical equations is on the writing of correct chemical formulas. Once the formula is correct, everything follows smoothly. The basic step is simply the examination of the number of atoms involved in the reaction.
Example: Ferric oxide is formed by the action of oxygen gas in iron.
Fe + O₂ --> Fe₂O₃

Notice that we write oxygen as O₂. We always do that. This is also true for hydrogen, nitrogen, chlorine, bromine, etc. Let us balance the chemical equation.
We begin first with atoms excluding oxygen or hydrogen. So we look at Fe and observe that there is one (1) on the left and two (2) on the right. What do we do? Right! We place 2 as the coefficient of Fe on the left. Now, we have:
2Fe + O₂ --> Fe₂O₃

So far the Fe is balanced. But, what about oxygen atom, O? We have 2 on the left and 3 on the right? What do we do? We get the least common multiple of 2 and 3 which happens to be 6. To make the total number of O atoms on the left equal to 6 we need to multiply it by 3. Therefore, we place 3 as the coefficient of O₂ on the left. To make the number of O atoms on the right equal to 6, we need to multiply 3 by 2. Therefore we place 2 as the coefficient of Fe₂O₃ on the right. Now, we have:
2Fe + 3O₂ --> 2Fe₂O₃

Then, we check. Wait a minute! The number of Fe atoms on the left is 2 while there are 4 Fe atoms on the right. What then shall we do? Yes. We need to change the coefficient of Fe on the left to 4. Now, let's examine what we have:
4Fe + 3O₂ --> 2Fe₂O₃

Left: 4 atoms Fe, 6 atoms O Right: 4 atoms Fe, 6 atoms O. The equation is now balanced.
Ok. It is your turn. Here is an exercise: Zinc metal is dropped to a test tube containing Hydrochloric acid. Write the balanced chemical equation. Go ahead, try it. When you are through, check your answer here.
Let's have another example: Calcium sulfate reacts with Lithium nitrate to form Calcium nitrate and Lithium sulfate. Here is the chemical equation:
CaSO₄ + LiNO₃ --> Ca(NO₃)₂ + Li₂SO₄

Let's balance the equation. There is 1 Li on the left but 2 on the right. We put 2 as the coefficient of LiNO₃ on the left. We now have:
CaSO₄ + 2LiNO₃ --> Ca(NO₃)₂ + Li₂SO₄

Let us examine. It seems that the above equation is already balanced! Now, try this exercise: Barium nitrite reacts with Aluminum sulfate. Write the balanced equation. Answer it and check if you have the correct answer here.
One last example before we move on. Combustion is simply a reaction with oxygen. Common combustion process involves hydrocarbons (compounds containing only hydrogen and carbon). The product of complete combustion in this case is carbon dioxide and water. Balancing this type of reactions is sometimes tricky. All you need to follow however is the sequence: 1)Balance the carbon 2)Balance the hydrogen 3)Balance the oxygen. An example: Methane (CH₄) gas is burned. Here is the chemical equation:
CH₄ + O₂ --> CO₂ + H₂O

To balance. Balance the C atoms. Ok balanced. Balance the H atoms. There are 4 on the left and 2 on the right. Put 2 as the coefficient of H₂O on the right. We now have:
CH₄ + O₂ --> CO₂ + 2H₂O

Then, balance the oxygen. We have 2 on the left, but 4 on the right. We palce 2 as the coefficient of O₂ on the left. This is now our equation:
CH₄ + 2O₂ --> CO₂ + 2H₂O

Let's check. Left: C = 1, H = 4, O =4 Right: C = 1, H = 4, O =4. The equation is now balanced. Now, here is a challenge for you. Write the balanced equation for the complete combustion of propylene gas (C₃H₆). Answer can be found here.

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