What constraints does the law of conservation of matter place on chemical equations?

When we balance equations, we need to make sure that the same number of atoms of each element is present on each side of the equation. The reason for this is that during a chemical process, the atoms rearrange, but aren't either created or destroyed. As a result, to keep with the law of conservation of mass, you've got to do the balancing.

Here is a video which discusses the importance of balancing a chemical equation. Video from: Noel Pauller

OK.