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Physical and Chemical Changes

Learn about physical and chemical changes, including physical properties, evidence of physical change, chemical properties, evidence of chemical change, and types of chemical reactions. Understand the role of energy in these processes.

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Physical and Chemical Changes

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  1. Physical and Chemical Changes

  2. Physical Property • Observable traits that do not change the identity of the substance • Include color, shape, smell, taste, mass, volume and density • Also include ductility, malleability, conductivity and solubility • Can be determined without changing a substance

  3. Physical Property • Density - mass/volume • Ductility – ability to be pulled into wire • Malleability – ability to be hammered • Conductivity – ability to pass electric current • Solubility – ability to dissolve

  4. Physical Change • Any change in size, shape, form, or state where the identity of the matter stays the same • Ex. - Cutting a watermelon into slices • Often easy to reverse with filtration, magnetism, evaporation, distillation, and centrifuge

  5. Physical Change • Evidence includes: • same substance • no new substances • color change • state change • same smell, taste, texture • different volume, mass • same density

  6. Chemical Property • The characteristic of a substance that allows it to change into something different • Includes flammability, reactivity with oxygen, and acidity • Testing for chemical properties causes a change in the substance

  7. Chemical Property • Flammability – able to be burned; combustion • Reactivity with oxygen • Acidity • pH level • scale from 1 to 14 • 1 being most acidic • 14 being least acidic (most basic) • Water is a 7 (neutral) on the pH scale

  8. Chemical Change • Happens when a substance undergoes a change that causes it traits to change • Ex. - digestion, photosynthesis, paint drying, and oil burning. • New materials are formed that are different from the starting materials

  9. Chemical Change • NOT easily reversed • Evidence includes: • Release of energy – light, heat, sound • Formation of gas or solid that is NOT the results of simple state change

  10. Chemical Change • Evidence includes: • new substance

  11. Example of Chemical Change • Chlorine • Added to swimming pools and drinking water • Causes acidity • Prevents reproduction, growth and development of algae, bacteria, protists and insects.

  12. Types of Chemical Reactions • Synthesis • Decomposition

  13. Acids and Bases • Acids • Sharp smell, sour taste • Corrode metals, harmful to organisms • pH between 0 and 7 • Ex. - citrus fruits contain acids. • Bases • Feel slippery, taste bitter • May also be harmful to organisms • pH of between 7 and 14 • Ex. - a bar of soap is basic

  14. Salts • Salts are compounds of metal and nonmetal • Formed when acids and bases react • Ex. – table salt and chalk

  15. Energy… • …is required for both types of changes

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