balancing equations
When the coefficients in a chemical equation are balanced, there are equal numbers of atoms of each element on both sides of the equation. We say that the chemical equation is balanced. You might ask, well, why does the chemical equation have to be balanced? Well, the answer to this stems from the atomic theory. In a chemical reaction, there is only a recombination of the atoms, no atoms are destroyed or created. Take our first equation:
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balanced equation for salt
In this reaction you have 2 atoms of sodium + 1 molecule of chlorine reacting to form 2 molecules of sodium chloride, which is salt.
In our next example we have:
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unbalanced equation example
Since the coefficients that give us the number of molecules have not yet been determined, this chemical equation is not balanced. To balance this equation, we select coefficients that will make the numbers of atoms of each element equal on both sides of the equations. It is best to write the coefficients so that they are the smallest whole numbers possible. To balance the previous equation we first want to look at the pieces which comprise the overall chemical equation. We find that oxygen occurs in only one of the products, so it would probably be the easiest to balance first. We get:
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balanced equation example
Doing this also balanced the number of P and H atoms. So this means that in just one step we arrived at the balanced equation. You see, we now have 12 atoms of oxygen, 12 atoms of hydrogen, and 4 atoms of phosphorus on both sides of the equation. Before we balanced the equation, we had 3 atoms of oxygen, 3 atoms of hydrogen, and 1 atom of phosphorus on the reactants side, and 4 atoms of oxygen, 6 atoms of hydrogen, and 2 atom of phosphorus on the products side.