1. C3H8 + 5O2 -> 3CO2 + 4H2O
2. Al2(SO3)3 + NaOH -> Na2SO3 + Al(OH)3
3. 4Al2O3 + 9Fe -> 3Fe3O4 + 8Al
4. KClO3 g KCl + O2
5. NH4NO3 g N2O + H2O

The Law of Conservation of Mass (or Matter) in a chemical reaction can be stated thus: In a chemical reaction, matter is neither created nor destroyed. It was discovered by Antoine Laurent Lavoisier (1743-94) about 1785.

An element is a substance that is made entirely from one type of atom. For example, the element hydrogen is made from atoms containing a single proton and a single electron. If you change the number of protons an atom has, you change the type of element it is. A compound is a substance formed when two or more chemical elements are chemically bonded together. Two types of chemical bonds common in compounds are covalent bonds and ionic bonds. The elements in any compound are always present in fixed ratios.