Presentation on theme: "Chemical and Physical Changes and Reactions"— Presentation transcript:
1 Chemical and Physical Changes and Reactions 8th grade ScienceChemical and Physical Changes and Reactions
2 Chemical ChangesChemical reactions are taking place all around you and even within youChemical reaction-a change in which one or more substances are converted into new substances (due to rearrangement)Reactants-substances that reactProducts-new substances produced
3 Chemical ChangesChemical changes occur when a material changes from one substance to anotherSeveral factors can indicate a chemical change has occurred:1. Color change2. Temperature change3. Production of a gas4. Formation of a solid
4 Physical changesPhysical changes: those changes that occur in nature involving a change in STATE only (phase changes)A substance may change states of matter as a result of a physical change, but will not become a new substanceEx: freezing, melting, evaporating, tearing, etc.
5 Conservation of MassLavoisier-famous scientist who discovered that masses of reactants and products were the same in an experimentSO, he concluded:Law of Conservation of Mass-the starting mass of reactants equals the final mass of the products ORMatter is neither created nor destroyed during chemical reactions
6 A metal will replace any less active metal Notice: copper, silver and gold-least active metalsSO: that is why these elements often occur as deposits of the relatively pure element.
7 All chemical reactions release or absorb energy This energy can take many forms, such as heat, light, sound and electricityChemical bonds are the source of this energy
8 When chemical reactions take place, some chemical bonds in the reactants must be broken Breaking these bonds takes energyBond formation releases energy
9 Exothermic Reaction- when the energy given off in a reaction is primarily in the form of heat *Exothermic reactions provide most of the power used in homes and industries
10 Endothermic reaction- when the energy needed is in the form of heat (Endothermic can also refer to phase/physical changes as well)