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Physical or Chemical Changes in Science: Understanding the Difference

This lesson focuses on determining whether a change is physical or chemical, and understanding the key differences between the two. Examples and explanations of physical and chemical changes are provided.

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Physical or Chemical Changes in Science: Understanding the Difference

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  1. SPI 0807.9.8 Physical or Chemical Changes Notes Date Learning Intention: Determine whether a physical or chemical change has occurred. Purpose: to understand the difference between physical changes and chemical changes. Success Criteria: I will show that I understand this by passing the quiz with a 90 or higher. I Can Statement: By the end of this unit I will be able to say... ...I can describe the key differences between a physical change and a chemical change.

  2. SPI 0807.9.8 Physical or Chemical Changes Notes Science Physical Changes • A change of matter from one form to another without a change in chemical properties. • Changes the appearance of an object, but does not change the composition of the object. • In other words, the way it looks is changed, but what it is does not change. (like dressing up for a costume party) • Physical changes do not form new substances. • Can be fairly easily undone or reversed

  3. SPI 0807.9.8 Physical or Chemical Changes Science Notes Physical Change: It looks different, but is still the same material. No chemical reaction has occurred. Example:Changes of state ARE NOT chemical reactions In other words, liquid to solid to gas are only physical changes Water Vapor Liquid Water Solid Water H2O H2O H2O

  4. SPI 0807.9.8 Physical or Chemical Changes Notes Science Examples of Physical Change • Melting • Freezing • Boiling • Bending • Cutting • Crushing • Tearing • Breaking • Smashing • Dissolving In every example here, the appearance is changed, but the composition remains the same. No Chemical Change Occurs! Dissolving Students often get confused about this one. Dissolving Kool-Aid in water is a physical change

  5. Physical Change Examples • Melting The appearance is changed, but the composition remains the same. • Freezing No Chemical Change! • Boiling

  6. Physical Change Examples • Cutting The appearance is changed, but the composition remains the same. • Crushing No Chemical Change! • Tearing

  7. Physical Change Examples • Breaking The appearance is changed, but the composition remains the same. • Smashing No Chemical Change! • Dissolving

  8. Chemical Changes • Is the result of a chemical reaction • A new substance is formed • CANNOT be easily undone or reversed 5 Key Points About Chemical Reactions 1) A new substanceis formed by rearranging the atoms. 2) The properties of the new substance are different from the substances that you started with. 3) No atoms are created or destroyedin chem reactions. 4) Atomic bonds are broken and new bonds are formed (at the valence electron level). 5) Compounds are formed during chemical reactions .

  9. Chemical Change Example Iron and oxygen react to form a compound called iron oxide. • Color Change: From silvery-gray to red-orange-brown Commonly Called Rust 1966 VW Beetle Bare Metal-No Paint 1966 VW Beetle Rusting away Chemical Equation 2Fe + 3O2 2FeO3

  10. Chemical Change Example Copper + oxygen react to form a compound called copper oxide. • Color Change: From golden-brown to aqua-marine green Also Called Rust Statue of Liberty Modern look-2014 Statue of Liberty Original look-1886 Chemical Equation 4Cu + O2 2Cu2O

  11. Chemical Change Example The Space Shuttle used solid rocket propellant called APCP • Burning APCP results in a very powerful chemical reaction Space Shuttle (USA) Lift Off Space Shuttle (USA) Lift Off Chemical Equation 10Al + 6NH4ClO4 4Al2O3 + 2AlCl3 + 12H2O + 3N2

  12. Chemical Change Example Upset stomach? You can take Alka Seltzer effervescent tablets • Drop the tablets in water and you get a chemical reaction Chemical Equation 3NaHCO3 + C6H8O7 Na3C6H5O7 + 3CO2 + 3H2O

  13. Chemical Change Example Soured milk is the result of a chemical reaction • Bacteria converts lactose to lactic acid Chemical Equation C12H22O11 + H2O 4C3H6O3

  14. SPI 0807.9.8 Physical or Chemical Changes Science Questions Note: It is asking about a physical change. Examples: melting, freezing, boiling, bending, cutting, crushing, tearing, breaking, smashing, and/or dissolving.

  15. SPI 0807.9.8 Physical or Chemical Changes Physical Change Examples: melting, freezing, boiling, bending, cutting, crushing, tearing, breaking, smashing, and/or dissolving. Science Questions Key Word

  16. One Key Point About Chemical Reactions • new substances are formed SPI 0807.9.8 Physical or Chemical Changes Science Questions Three Chemical Change Indicators (1) temperature change, (2) gas/odor, (3) liquid to solid while heating up

  17. One Key Point About Chemical Reactions • new substances are formed SPI 0807.9.8 Physical or Chemical Changes Science Questions Started with Copper Carbonate. Ended up with Copper Oxide.

  18. Note: It is asking about a physical change. SPI 0807.9.8 Physical or Chemical Changes Science Questions Examples: melting, freezing, boiling, bending, cutting, crushing, tearing, breaking, smashing, and/or dissolving. It merely changed color as the blue powder dissolved. (Temp unchanged.)

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