During chemical reactions, mass is conserved. This is because no atoms are created or destroyed, rather they are rearranged. A chemical equation needs to show conservation of mass. The number of each type of atom needs to be the same on both sides of the yield sign. If it is not, the equation needs to be balanced by using coefficients. This Powerpoint presentation explores conservation of mass and illustrates how to achieve it by balancing. The presentation ends with several practice problems.
Free worksheets for this topic are available on my website at http://www.evanschemistrycorner.com.