Chemical%20Reaction%20 - PowerPoint PPT Presentation

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Chemical%20Reaction%20

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Describing Chemical Reactions (Section 8-1) Chemical Reaction any process which results in the formation of one or more new substances having different physical ... – PowerPoint PPT presentation

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Title: Chemical%20Reaction%20


1
Describing Chemical Reactions
(Section 8-1)
  • Chemical Reaction any process which results
    in the formation of one or more new substances
  • having different physical and chemical properties
    than the original substance(s).

2
Evidence of Chemical Change
  • Changes in Energy
  • release of light
  • production of sound
  • release of heat
  • absorption of heat
  • absorption or release
  • of electrical energy
  • Changes in Substance
  • change in color
  • change in odor
  • formation of a gas
  • formation of a precipitate (insoluble solid)

changes in temp
may also occur in physical change
3
Verifying a chemical change
  • physical changes can often be (easily) reversed
    (heat ice to
    melt to liquid, remove heat to refreeze)
  • chemical changes are often irreversible
    , or require other chemical
    reactions to restore the original substance.
  • when tested, the new substances exhibit different
    properties (density,
    reactivity)

4
Requirements of Reactions
  • 1. energy changes
  • a. emission (release) of energy
  • ? exothermic
  • ? energy is a product
  • ( butane oxygen ? carbon dioxide water
    energy )
  • b. absorption of energy
  • ? endothermic
  • ? energy is a reactant
  • ( sodium chlorate energy ? sodium chloride
    oxygen )
  • 2. reactant atoms and/or molecules must collide
  • ? w/ proper energy
  • ? w/ correct orientation

5
Chemical Equations are recipes for reactions
  • ? Word Equations do not provide information
    about proportions (amounts)
  • sodium chlorate ? sodium
    chloride oxygen
  • reactant(s)
    yields product(s)
  • ? Formula Equations provide information about
    proportions (amounts) / states / reaction
    conditions

  • heat
  • 2 NaClO3 (s) ? 2 NaCl (s)
    3 O2 (g)
  • coefficients used to balance numbers/moles of
    atoms to comply with law of conservation of
    matter
  • Table 2 (p. 265) symbols used frequently in
    equations to provide information about reaction
    conditions

6
(s), ?
7
Homework Section 8-1 Review (p. 266) 2, 3, 4,
7, 8, 9, 10
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