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