The number of __________ must be equal on both sides of the ___________________. Reactions must be balanced because all things in nature need to be ___________________. There are __________________ rules that we follow when balancing reactions. The __________________ should never changed but only the __________________ can be changed when balancing the reaction. We are allowed to use __________________ or __________________ for the coefficients to balance a reaction. We must avoid _______________________ when balancing a reaction and only do ___________atom at a time.