Unit 6: Chemical Reactions

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Unit 6 Chemical Reactions

• Chapter 9

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Unit 6 Chemical Reactions

• The Nature of Chemical Reactions (9-1)
• A. Definition process in which 1 or more
  substances are converted to new substances with
  different chemical and physical properties
• B. Common Examples
• C. Components
• 1. Reactant substance that enters a chemical
  reaction
• 2. Product substance that is produced from a
  chemical reaction

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• D. Reason for Reactions
• Depends on valence electrons energy
• II. Chemical Equations (9-2)
• A. Definition sentences that represent
  reactions
• B. Indicates what substances are involved in
  the reaction how many

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• C. Types of Equations
• 1. Word Equations
• a. Name chemicals involved in the reaction
• b. Only a qualitative description
• Ex hydrogen oxygen ? water
• (reactants) (yields) (product)
• 2. Formula Equations
• a. Gives the formulas of the chemicals
  involved and the ratios

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• b. Gives a quantitative description
• Ex H2 O2 ? H2O
• (reactants) (yields) (product)
• This is not balanced, it must be! Why?
• Law of Conservation of Mass/Atoms in ordinary
  chemical reactions
• 1.) Total mass of reactants is equal to
  total mass of products

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• 2.) Number of elements for reactants is equal to
  the number of elements for products
• Atoms are not created nor destroyed, but they
  simply rearrange.
• Coefficients numbers in front of the formulas
  in chemical equations that give the ratios of the
  substances involved in the reaction

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• Ex 2H2 O2 ---gt 2H2O
• 2 molecules 1 molecule 2 molecules
• or
• 2 moles 1 mole 2 moles
• Ex Interpret the following chemical reaction
• 2 NaI Cl2 ---gt 2NaCl I2
• Note What is the difference between 2CO and
  CO2

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• D. Writing and Balancing Chemical Equations
• 1. Review Indicate how many atoms of each
  element are present in the following
• a. 5NH3 ---gt
• b. 4Ca(OH)2 ---gt
• c. 3BaSO4 ---gt

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• 2. Review Diatomics (H2,O2,N2,Cl2,F2,Br2,I2)
• Exist as a molecule of 2 atoms when they are by
  themselves (natural/elemental form)
• 3. Steps to writing chemical equations
• a. Write the correct chemical formulas for
  compounds involved in the reaction
• All compounds should have a neutral charge-
  subscripts are used to balance the charge on
  ionic compounds

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• b. Balance equation according to the law of
  conservation of atoms coefficients are used
• c. Indicate the phase of each compound
• (s) ---gt solid
• (l) ---gt liquid
• (g) ---gt gas
• (aq) ---gt solid salt dissolved in water
• d. Show the energy change in the equation
• Endothermic ---gt Energy written on left side
• Exothermic ---gt Energy written on right side

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• III. Classifying Chemical Reactions (9-3)
• 1. Synthesis (S), Composition, or Direct
  Combination two or more substances combine to
  form a more complex substance
• General Form A B ---gt AB
• Examples 2H2 O2 ---gt 2H2O
• 4Fe 3O2 ---gt 2Fe2O3 (rusting)
• 2CO O2 ---gt 2CO2

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• 2. Decomposition (D) a complex substance breaks
  down to form two or more simple substances
• General Form AB ---gt A B
• Examples 2H2O ---gt 2H2 2O2
• 2KClO3 ---gt 2KCl 3O2
• 2HgO ---gt 2Hg O2

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• 3. Single Replacement (SR) one element is
  replaced in a compound by another element
• General Form A BX ---gt AX B
• or
• Y BX ---gt BY X
• Examples Fe CuSO4 ---gt FeSO4 Cu
• Cl2 2KI ---gt 2KCl I2
• Cu AgNO3 ---gt CuNO3 Ag

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• 4. Double Replacement (DR) or Ionic ionic
  compounds swap partners/pairings
• General Form AB XY ---gt AY XB
• Examples NaCl AgNO3 ---gt NaNO3 AgCl
• Ba(OH)2 NaBr --gt BaBr2 2NaOH
• (NH4)2CO3 CaCl2 --gt 2NH4Cl CaCO3