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Chemical and Physical Changes and Reactions

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Presentation on theme: "Chemical and Physical Changes and Reactions"— Presentation transcript:

1 Chemical and Physical Changes and Reactions
8th grade Science Chemical and Physical Changes and Reactions

2 Chemical Changes Chemical reactions are taking place all around you and even within you Chemical reaction-a change in which one or more substances are converted into new substances (due to rearrangement) Reactants-substances that react Products-new substances produced

3 Chemical Changes Chemical changes occur when a material changes from one substance to another Several factors can indicate a chemical change has occurred: 1. Color change 2. Temperature change 3. Production of a gas 4. Formation of a solid

4 Physical changes Physical 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 substance Ex: freezing, melting, evaporating, tearing, etc.

5 Conservation of Mass Lavoisier-famous scientist who discovered that masses of reactants and products were the same in an experiment SO, he concluded: Law of Conservation of Mass-the starting mass of reactants equals the final mass of the products OR Matter is neither created nor destroyed during chemical reactions

6 A metal will replace any less active metal
Notice: copper, silver and gold-least active metals SO: 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 electricity Chemical 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 energy Bond 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)

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