How is balancing a chemical reaction related to the law of conservation of matter?

Answer 1

When you balance an equation, you're trying to arrange it so that for each atom, there are as many of that atom in the end as there were in the beginning. For instance, in the reaction in which oxygen and hydrogen combine to make water, the unbalanced equation is O2 + H2 --> H2O. The balanced version is O2 + 2H2 --> 2H2O. In the unbalanced version, you started with two O atoms, but you finished with only one. This is not allowed under the law of conservation of matter--you can't just destroy an atom. So you have to balance it with the second equation, in which you have four H atoms and two O's at all times.

Answer 2

Matter is neither created or destroyed. You should have the same amounts of atoms in your products and reactants.