An example of the law of conservation of mass is the combustion of a piece of paper to form ash, water vapor and carbon dioxide. In this process, the mass of the paper is not actually destroyed; instead, it is transformed into other forms. This best demonstrates the law that states matter cannot be created or destroyed. However, the form of matter can be changed.
If the total mass of the compounds resulting from burning the paper are weighed, it still equals the mass of the paper. In a chemical reaction, two molecules of hydrogen gas (H) combine with one molecule of oxygen gas (O2) to form one molecule of water (H2O). Evidently, no matter has been destroyed. Another example that illustrates this law is the heating of 10 grams of calcium carbonate (CaCo3), which produces 4.4 grams of carbon dioxide (CO2) and 5.6 grams of calcium oxide (CaO). In this chemical reaction, the total mass of the resultant products is equal to the total mass of the reactants.
The law of conservation of energy is similar to that of conservation of mass. When an electric heater is turned on, the electrical energy is converted into heat energy. If the amount of electricity supplied to the heater is measured, it equals the amount of heat produced by the heater. This emphasizes the fact that energy cannot be created or destroyed but only changed.