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Changes in Matter

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Chapter Seventeen: Chemical Reactions 17.1 Understanding Chemical Reactions 17.2 Energy and Chemical Reactions Investigation 17B How do scientists describe what ... – PowerPoint PPT presentation

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Title: Changes in Matter


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Changes in Matter
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Chapter Seventeen ChemicalReactions
  • 17.1 Understanding Chemical Reactions
  • 17.2 Energy and Chemical Reactions

4
Investigation 17B
Conservation of Mass
  • How do scientists describe what happens in a
    chemical reaction?

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17.2 Energy and chemical reactions
  • All chemical reactions involve energy.
  • Burning is a chemical reaction that gives off
    energy in the form of heat and light.
  • In plants, photosynthesis is a reaction that uses
    energy from sunlight.

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17.2 Types of energy in reactions
  • If forming new bonds releases more energy than it
    takes to break the old bonds, the reaction is
    exothermic.
  • Exothermic reactions tend to keep going because
    each reaction releases enough energy to start the
    reaction in neighboring molecules.

How can the energy from an exothermic reaction be
useful?
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17.2 Types of energy in reactions
  • Endothermic reactions absorb energy.
  • These reactions need energy to keep going.

Where does the energy needed for this reaction
come from?
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17.2 Activation energy
  • Activation energy is the energy needed to start a
    reaction and break chemical bonds in the
    reactants.
  • This is why a flammable material, like gasoline,
    does not burn without a spark or flame.
  • The spark supplies the activation energy to start
    the reaction.

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17.2 Activation energy
  • This diagram shows how the energy flows in the
    reaction of hydrogen and oxygen.

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17.2 Addition reactions
  • In an addition reaction, two or more substances
    combine to form a new compound.
  • The process of creating large molecules from
    small ones is called polymerization.

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17.2 Decomposition reactions
  • A chemical reaction in which a single compound is
    broken down to produce two or more smaller
    compounds is called a decomposition reaction.

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17.2 Reaction symbols
  • The small symbols in the parentheses (s, l, g,
    aq) next to each chemical formula indicate the
    phase of each substance in the reaction.

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17.2 Displacement reactions
  • In single-displacement reactions, one element
    replaces a similar element in a compound.

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17.2 Precipitation reactions
  • A precipitate is a new solid product that comes
    out of solution in a chemical reaction.
  • The formation of a cloudy precipitate is evidence
    that a double-displacement reaction has occurred.

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17.2 Precipitation
  • The limewater test for carbon dioxide is a
    precipitation reaction.

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17.2 Petroleum refining
  • The refining process separates petroleum into
    molecules with different numbers of carbon atoms.

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17.2 Petroleum refining
  • These are some of the molecules found in gasoline.

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17.2 Combustion reactions
  • In a perfect reaction, all the hydrocarbon
    molecules are completely burned to into carbon
    dioxide and water.
  • In an engine not all the fuel burns completely
    and pollutants such as carbon monoxide are also
    formed.

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17.2 Nuclear reactions
  • Nuclear reactions change the nucleus of an atom.
  • Because they affect the nucleus itself, nuclear
    reactions can change one element into a different
    element.

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Chemistry Connection
How do Hot and Cold Packs Work?
Have you ever used a hot or cold pack? Although
its seem like magic, its really a mini
chemistry lab inside that plastic wrapper.
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Activity
Explore Hot and Cold Packs
  • Most hot and cold packs work by breaking a
    membrane that separates a solid and water.
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