Combustion, or , is an example of one of the most familiar chemical changes. melting of ice, likewise, is one of the most common examples of physical changes. when a piece of coal burns, combines with the carbon in the coal. the products are carbon dioxide gas, water vapor, and a lot of ash. after careful measurements are taken, the of the reactants (coal and oxygen) is to the mass of the products (carbon dioxide, water vapor, and ash). during the reaction, the quantity of matter is unchanged. similarly, when 10 grams of ice , grams of water is obtained. mass is in this change as well.