Chapter 3   Chemical Reactions
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Chapter 3 Chemical Reactions

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Chapter 3   Chemical Reactions Chapter 3 Chemical Reactions Presentation Transcript

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