text: In a chemical reaction, the quantity of each element does not change. Thus, each side of the equation must represent the same quantity of any particular element. Also in case of net ionic reactions the same charge must be present on both sides of the equation. Then, and only then, the equation is balanced. Given an unbalanced equation, one may balance it by changing the scalar number for each molecular formula.\n\nSimple chemical equations can be balanced by inspection, that is, by trial and error. Generally, it is best to balance the most complicated molecule first. Hydrogen and oxygen are usually balanced last.\n\nEx #1. Na + O2 → Na2O\n\nIn order for this equation to be balanced, there must be an equal amount of Na on the left hand side as on the right hand side. As it stands now, there is 1 Na on the left but 2 Na's on the right. This problem is solved by putting a 2 in front of the Na on the left hand side:\n\n    2Na + O2 → Na2O\n\nIn this equation there are 2 Na atoms on the left and 2 Na atoms on the right. In the next step the oxygen atoms are balanced as well. On the left hand side there are 2 O atoms and the right hand side only has one. This is still an unbalanced equation. To fix this a 2 is added in front of the Na2O on the right hand side. Now the equation reads:\n\n    2Na + O2 → 2Na2O\n\nNotice that the 2 on the right hand side is "distributed" to both the Na2 and the O. Currently the left hand side of the equation has 2 Na atoms and 2 O atoms. The right hand side has 4 Na's total and 2 O's. Again, this is a problem, there must be an equal amount of each chemical on both sides. To fix this 2 more Na's are added on the left side. The equation will now look like this:\n\n    4Na + O2 → 2Na2O\n\nThis equation is a balanced equation because there is an equal number of atoms of each element on the left and right hand sides of the equation.\n\nEx #2. P4 + O2 → P4O10\n\nThis equation is not balanced because there is an unequal amount of O's on both sides of the equation. The left hand side has 4 P's and the right hand side has 4 P's. So the P atoms are balanced. The left hand side has 2 O's and the right hand side has 10 O's. To fix this unbalanced equation a 5 in front of the O2 on the left hand side is added to make 10 O's on both sides resulting in\n\n    P4 + 5O2 → P4O10\n\nThe equation is now balanced because there is an equal amount of substances on the left and the right hand side of the equation.\n\nEx #3. C2H5OH + O2 → CO2 + H2O\n\nThis equation is more complex than the previous examples and requires more steps. The most complicated molecule here is C2H5OH, so balancing begins by placing the coefficient 2 before the CO2 to balance the carbon atoms.\n\n    C2H5OH + O2 → 2CO2 + H2O\n\nSince C2H5OH contains 6 hydrogen atoms, the hydrogen atoms can be balanced by placing 3 before the H2O:\n\n    C2H5OH + O2 → 2CO2 + 3H2O\n\nFinally the oxygen atoms must be balanced. Since there are 7 oxygen atoms on the right and only 3 on the left, a 3 is placed before O2, to produce the balanced equation:\n\n    C2H5OH + 3O2 → 2CO2 + 3H2O