You can balance reactions easily by first looking at the subscripts (or the little numbers in the reaction). Then list down each of their values to know which are not yet equal from both sides of the equation. Then, think of the numbers that you can multiply with each of the compounds to balance the reaction. For example: C3H8 + O2 ---> H2O + CO2. Take note that in the reactants, C has 3, H has 8 and O has 2. In the products, H has 2, O has 3 and C has 1. So first, we balance the C and H: We multiply CO2 by 3 to make the no. of C in the products be equal to the reactants. Then we multiply H2O by 4 to balance the no. of H in the equation. Lastly, we now have a total of 10 O in the products, so we multiply O2 by 5. Now we have: C3H8 + 5O2 --> 4H2O + 3CO2.