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Lecture 2.4- Chemical Changes

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Section 2.4 lecture for Honors & Prep Chemistry

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Lecture 2.4- Chemical Changes

  1. 1. BELLWORK Element, compound, or mixture? <ul><li>Classify the following materials as an element compound or mixture. Give reasons for your answers . </li></ul><ul><li>Table salt (NaCl) </li></ul><ul><li>Salt water </li></ul><ul><li>Apple juice </li></ul><ul><li>Water (H 2 O) </li></ul><ul><li>Helium gas (He) </li></ul>
  2. 2. Lecture 2.4- Chemical changes
  3. 3. <ul><ul><ul><li>A magnet separates iron from sulfur. </li></ul></ul></ul><ul><ul><li>During a physical change , the composition of matter never changes. </li></ul></ul>Physical Changes
  4. 4. Chemical Changes <ul><ul><ul><li>A mixture of iron and sulfur is heated. </li></ul></ul></ul><ul><ul><ul><li>The iron and sulfur react and form iron sulfide. </li></ul></ul></ul><ul><ul><li>During a chemical change , the composition of matter ALWAYS changes. </li></ul></ul>
  5. 5. Recognizing Chemical Changes <ul><ul><li>It is usually a chemical change if there is : </li></ul></ul>
  6. 6. Recognizing Chemical Changes <ul><ul><li>It is usually a chemical change if there is : </li></ul></ul><ul><ul><ul><li>a transfer of energy (ex. heat or light) </li></ul></ul></ul>
  7. 7. Recognizing Chemical Changes <ul><ul><li>It is usually a chemical change if there is : </li></ul></ul><ul><ul><ul><li>a transfer of energy (ex. heat or light) </li></ul></ul></ul><ul><ul><ul><li>a change in color </li></ul></ul></ul>
  8. 8. Recognizing Chemical Changes <ul><ul><li>It is usually a chemical change if there is : </li></ul></ul><ul><ul><ul><li>a transfer of energy (ex. heat or light) </li></ul></ul></ul><ul><ul><ul><li>a change in color </li></ul></ul></ul><ul><ul><ul><li>production of a gas </li></ul></ul></ul>
  9. 9. Recognizing Chemical Changes <ul><ul><li>It is usually a chemical change if there is : </li></ul></ul><ul><ul><ul><li>a transfer of energy (ex. heat or light) </li></ul></ul></ul><ul><ul><ul><li>a change in color </li></ul></ul></ul><ul><ul><ul><li>production of a gas </li></ul></ul></ul><ul><ul><ul><li>formation of a precipitate. </li></ul></ul></ul>
  10. 10. <ul><ul><ul><li>A precipitate is a solid that forms and settles out of a liquid mixture. </li></ul></ul></ul>
  11. 11. <ul><ul><ul><ul><li>A chemical change is also called a chemical reaction . </li></ul></ul></ul></ul>
  12. 12. <ul><ul><ul><ul><li>A chemical change is also called a chemical reaction . </li></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>A substance present at the start of the reaction is a reactant . </li></ul></ul></ul></ul></ul>
  13. 13. <ul><ul><ul><ul><li>A chemical change is also called a chemical reaction . </li></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>A substance present at the start of the reaction is a reactant . </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>A new substance created by the reaction is a product . </li></ul></ul></ul></ul></ul>
  14. 14. <ul><ul><ul><ul><li>A chemical change is also called a chemical reaction . </li></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>A substance present at the start of the reaction is a reactant . </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>A new substance created by the reaction is a product . </li></ul></ul></ul></ul></ul>Fe + S  FeS iron sulfur iron sulfide
  15. 15. <ul><ul><ul><ul><li>A chemical change is also called a chemical reaction . </li></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>A substance present at the start of the reaction is a reactant . </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>A new substance created by the reaction is a product . </li></ul></ul></ul></ul></ul>Fe + S  FeS iron sulfur iron sulfide Reactants Product
  16. 16. Chemical Changes <ul><ul><ul><li>The ability of a substance to undergo a specific chemical change is called a chemical property . </li></ul></ul></ul>
  17. 17. Chemical vs. Physical Properties
  18. 18. Conservation of Mass <ul><ul><li>LAW of Conservation of Mass – </li></ul></ul><ul><ul><li>During any chemical reaction, the mass of the products is always equal to the mass of the reactants. </li></ul></ul>
  19. 19. <ul><ul><ul><li>The conservation of mass is easily observed when a change occurs in a closed container. </li></ul></ul></ul>
  20. 20. Conservation of Mass

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