Physical Changes Physical Change – a substance changes in form but not in chemical composition. In a physical change no new substance is produced. Particles are not joined at the molecular level. e.g. changing the shape of something e.g. freezing, boiling, melting e.g. dissolving

Chemical Changes Chemical Change – causes one or more new substances to be formed. A chemical change is difficult or impossible to reverse. In a chemical change , the new substances formed have different properties from those of the starting materials. Particles are joined at the molecular level. The starting materials in a chemical reaction are reactants and what is made from the chemical reaction are products. e.g. food cooking e.g. rusting of metal e.g. burning The Law of Conservation of Mass states: In a chemical reaction the total mass of the reactants is always equal to the total mass of the products. (Atoms are never created or destroyed, molecules are just rearranged.)

Indicators of Chemical Change If you observe two or more of the following occurrences, a chemical change has probably taken place. heat is produced (exothermic reaction) heat is absorbed (endothermic reaction) there is a change in colour a gas is produced a precipitate forms in a liquid the starting material is used up a material with new properties forms the change is difficult to reverse