Performing material balance on systems involving reactions is a very important subject matter in Process Calculations. There are three methods to solve such a problem. Lecture 22 dealt with one of the methods namely molecular species balance. In this video Atomic Species Balance was taught with the help of two simple examples. Taking a balance on atomic species is very straightforward as it takes the simplest form of input = output. This happens because in a chemical reaction number of atoms of any element doesn't change. They just recombine with other atoms in different proportions. So number of atoms remain a conserved quantity and we can take a balance on atomic species. Usually there will be as many atomic species balance as the number of species present. However, if you can write one of the balance as a linear combination of other atomic balances, then that balance is not counted as independent balance equation. This concept was highlighted with the help of an example.