How to balance chemical equation


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Rather than just give you the balanced equation, I’m going to explain the process of actually balancing it;-

C4H10 + O2 = CO2 + H2O

This unbalanced equation represents the complete combustion of butane in oxygen to produce carbon dioxide and water.

Since there is only one product on the right-hand side of the equation which contains hydrogen (water), then all of the hydrogen in the butane will produce only water molecules. Butane has ten hydrogen atoms, so the water produced must contain 10 hydrogen atoms too. Therefore there must be five water molecules in the balanced equation. We can now write a new equation which is closer to the balanced state than the one we were first given;-

C4H10 + O2 = CO2 + 5 H2O

Okay, so now we’ve balanced the hydrogen. But looking at the new equation we can see that neither carbon nor oxygen are balanced. Since all of the carbon in the butane molecule ends up as CO2, we can use the same procedure for carbon as we did for hydrogen.

Four carbon dioxide molecules must be produced from one butane molecule, so we can therefore write a third equation which is balanced for both hydrogen and carbon;-

C4H10 + O2 = 4 CO2 + 5 H2O

Now, all that remains is to balance the oxygen on both sides of the equation.

There are two oxygen atoms on the left and a total of thirteen on the right. (8 from the CO2 and 5 from the H2O). But an oxygen molecule contains two oxygen atoms. How can we balance the uneven number of oxygen atoms on the right with a whole number of oxygen molecules on the left?

The easiest way is to multiply all the terms in the equation by two, which will give us an even number of oxygen atoms on both sides of the equation, while ensuring that both carbon and hydrogen still remain balanced;-

2 C4H10 + 2 O2= 8 CO2 + 10 H2O

The next step is to balance the 26 oxygen atoms on the right with an equivalent number of oxygen molecules on the left. Since 26 oxygen atoms represents 13 oxygen molecules, then all we need to do is change the number of oxygen molecules in the last equation to 13, which gives us;-

2 C4H10 + 13 O2 = 8 CO2 + 10 H2O

Now the equation is balanced for all elements. We have 8 carbon atoms, 26 oxygen atoms and 20 hydrogen atoms on the left…. and exactly the same number of each on the right.

Job done!

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