Chapter 3 Chemical Reactions


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Chapter 3 Chemical Reactions

  1. 1. Chemical Interactions <ul><li>Chapter 3: </li></ul><ul><li>Chemical Reactions </li></ul>
  2. 2. Section 3.1 Chemical Reactions Alter Arrangements of Atoms
  3. 3. Atoms interact in chemical reactions. <ul><li>Substances change in two ways. </li></ul><ul><ul><li>Physical changes: the substance does not change, but appearance or some properties might change. </li></ul></ul>
  4. 4. Page 71 <ul><ul><li>Chemical changes: a new substance is formed </li></ul></ul><ul><ul><ul><li>A chemical reaction rearranges atoms. </li></ul></ul></ul>
  5. 5. Page 71 Bonds are broken in reactants, and new bonds are formed in the products.
  6. 6. Page 72 Evidence of a chemical reaction includes a change in color or temperature or the formation of a precipitate or a gas .
  7. 7. Chemical reactions can be classified. <ul><li>A synthesis reaction combines two or more simpler reactants to form a new, more complex product. </li></ul>
  8. 8. Page 73 <ul><li>A decomposition reaction breaks a reactant into two or more simpler products. </li></ul>
  9. 9. Page 73 <ul><li>A combustion reaction always involves oxygen. The other reactant often contains carbon and hydrogen. </li></ul>
  10. 10. The rates of chemical reaction can vary. <ul><li>Four factors can change the rate of a chemical reaction. </li></ul><ul><ul><li>The concentration of reactants </li></ul></ul><ul><ul><li>The surface area of reactants </li></ul></ul><ul><ul><li>The temperature of the reaction mixture. </li></ul></ul>
  11. 11. Page 75
  12. 12. Page 76 <ul><li>continued </li></ul><ul><ul><li>The presence of a catalyst. </li></ul></ul><ul><ul><ul><li>The catalyst takes part in a reaction but is not consumed during the reaction. </li></ul></ul></ul><ul><ul><ul><li>It decreases the energy needed to start a reaction. </li></ul></ul></ul><ul><ul><ul><li>It increases the reaction rate. </li></ul></ul></ul><ul><ul><ul><li>Enzymes often work as catalysts in living things. </li></ul></ul></ul>
  13. 13. Page 76
  14. 14. Section 3.2 The Masses of Reactants and Products are Equal.
  15. 15. Careful observations led to the discovery of the conservation of mass. <ul><li>Antoine Lavoisier’s careful quantitative experiments showed that in a chemical reaction, the total mass of reactants is always equal to the total mass of products. </li></ul><ul><li>Law of conservation of mass : Mass is neither created nor destroyed during a chemical reaction. </li></ul>
  16. 16. Chemical reactions can be described by chemical equations. <ul><li>A chemical equation represents the way in which a reaction rearranges the atoms in chemicals. </li></ul><ul><li>To write an equation, you must know the reactants and products, their chemical formulas, and the direction of the reaction. C + O 2 CO 2 </li></ul><ul><li>The arrow in the equation indicates the direction of the reaction. </li></ul>
  17. 17. Chemical equations must be balanced. <ul><li>A chemical equation must reflect the law of conservation of mass. </li></ul><ul><ul><li>Each side of the equation must have the same number of atoms of each element. </li></ul></ul>
  18. 18. Page 81 <ul><li>An equation is balanced when the number of molecules of reactants or products represented equally on both sides of the equation. This equation is not balanced. </li></ul>
  19. 19. Page 81 <ul><li>Step 1: The equation is balanced by changing the amounts of reactants or products. </li></ul><ul><ul><li>Balance H: Add another H2O </li></ul></ul><ul><ul><li>Balance O: Add another O2 </li></ul></ul>
  20. 20. Page 81 <ul><li>Step 2: Simplify the balanced equation by using coefficients. </li></ul>
  21. 21. Page 82 <ul><li>When balancing an equation, subscripts in the chemical formulas of the reactants and products cannot be changed. </li></ul><ul><ul><li>Changing the subscript changes the substance represented. </li></ul></ul><ul><ul><li>O 2 = oxygen O 3 = ozone </li></ul></ul>
  22. 22. Page 83 <ul><li>Equations must be balanced by changing the coefficients , which changes only the amount of the reactants and products represented by the equation. </li></ul>
  23. 23. Let’s Practice! <ul><li> (rt. click/open) </li></ul>
  24. 24. Section 3.3 Chemical Reactions Involve Energy Changes.
  25. 25. Chemical reactions release and absorb energy. <ul><li>Chemical reactions break the chemical bonds in reactants and make new bonds in the products. </li></ul><ul><li>Breaking bonds releases energy. </li></ul><ul><li>The energy in chemical bonds is called bond energy. </li></ul>
  26. 26. Page 87 <ul><li>Exothermic reaction: </li></ul><ul><ul><li>More energy is released when the bonds in products form than is used to break the bonds in reactants. </li></ul></ul><ul><ul><li>Energy is released, often as heat. </li></ul></ul>
  27. 27. <ul><li>Exothermic reactions (cont.) </li></ul><ul><ul><li>Reactants have lower bond energies than products. </li></ul></ul><ul><ul><li>All common combustion reactions are exothermic. </li></ul></ul>Jellyfish glow because of exothermic chemical reactions.
  28. 28. Page 88
  29. 29. Page 88 <ul><li>Endothermic reaction: </li></ul><ul><ul><li>More energy is needed to break the bonds in reactants than is released when the bonds in products form. </li></ul></ul><ul><ul><li>The reactants have higher bond energies than the products. </li></ul></ul><ul><ul><li>Energy is absorbed. </li></ul></ul>Photosynthesis is an important endothermic reaction. 6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2
  30. 30. Page 89
  31. 31. Exothermic and endothermic reactions work together to supply energy. <ul><li>Endothermic and exothermic reactions can form a cycle. </li></ul><ul><ul><li>Example: The energy stored by the series of endothermic reactions in photosynthesis can be released by exothermic reactions such as combustion. </li></ul></ul>
  32. 32. A plant absorbs energy from the sun during photosynthesis. 6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2 Endothermic Equation If the plant burns, the energy is released. C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O Exothermic Reaction Combustion Page 90
  33. 33. Section 3.4 Life and Industry Depend on Chemical Reactions
  34. 34. Living things require chemical reactions. <ul><li>Photosynthesis is an endothermic process. </li></ul><ul><ul><li>Plants absorb energy from the sun. </li></ul></ul><ul><ul><li>The energy is stored in the chemical bonds of sugars. </li></ul></ul><ul><ul><li>The sugars break down during exothermic reactions of respiration, the process that produces energy for living organisms. </li></ul></ul>Photosynthesis: 6CO 2 + 6H 2 O + energy C 6 H 12 O 6 + 6O 2 Respiration: C 6 H 12 O 6 6CO 2 + 6H 2 O = energy
  35. 35. Page 95 <ul><li>Most reactions that take place in living organisms use enzymes, catalysts that cause reactions to take place at the relative temperatures of living tissue. </li></ul>
  36. 36. Chemical reactions are used in technology. <ul><li>Combustion engines use gasoline in a chemical reaction that releases energy. </li></ul>
  37. 37. Page 96 <ul><li>Catalytic converters are technological devices that remove unwanted pollutants from the burning of gasoline in automobile engines. </li></ul><ul><ul><li>Use metals as catalysts: platinum, palladium, rhodium </li></ul></ul><ul><ul><li>Catalysts allow reactions between exhaust gases to occur. </li></ul></ul><ul><ul><li>Convert pollutants into gases that are typical parts of Earth’s atmosphere: oxygen, nitrogen, water vapor, carbon dioxide. </li></ul></ul>
  38. 38. Page 97
  39. 39. Industry uses chemical reactions to make useful products. <ul><li>The electronics industry produces silicon for microchips by refining SiO2 (quartz) into pure silicon. </li></ul><ul><ul><li>Silicon treated with photoresist and light produces miniature electronic circuits. </li></ul></ul>
  40. 40. Page 99