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