Unit 6 Chemical Reactions by pptfiles


									Unit 6: Chemical
     Chapter 9
        Unit 6: Chemical Reactions
I.      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
 D. Reason for Reactions
     * Depends on: valence electrons &

II. Chemical Equations (9-2)
  A. Definition: sentences that represent

 B. Indicates: what substances are involved
 in the reaction & how many
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
     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
 2.) Number of elements for reactants is
 equal to the number of elements for

** 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
Ex: 2H2        +    O2           --->    2H2O

     2 molecules        1 molecule      2 molecules

     2 moles            1 mole          2 moles

Ex: Interpret the following chemical reaction
  2 NaI +       Cl2 ---> 2NaCl +         I2

** Note: What is the difference between 2CO
  and CO2
D. Writing and Balancing Chemical Equations

 1. Review: Indicate how many atoms of each
 element are present in the following:
    a. 5NH3 --->

    b.   4Ca(OH)2 --->

    c.   3BaSO4 --->
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
b. Balance equation according to the law of
    conservation of atoms – coefficients are

c. Indicate the phase of each compound
    (s) ---> solid
    (l) ---> liquid
    (g) ---> gas
    (aq) ---> solid salt dissolved in water

d. Show the energy change in the equation
    Endothermic ---> Energy written on left side
    Exothermic ---> Energy written on right side
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 ---> AB

 Examples:     2H2 + O2 ---> 2H2O
              4Fe + 3O2 ---> 2Fe2O3         (rusting)

               2CO + O2 ---> 2CO2
2. Decomposition (D) – a complex substance
  breaks down to form two or more simple

 General Form: AB ---> A + B

 Examples: 2H2O ---> 2H2 + 2O2
          2KClO3 ---> 2KCl + 3O2
           2HgO ---> 2Hg + O2
3. Single Replacement (SR) – one element is
  replaced in a compound by another element

 General Form: A + BX ---> AX + B
               Y + BX ---> BY + X

 Examples: Fe + CuSO4 ---> FeSO4 + Cu
           Cl2 + 2KI ---> 2KCl + I2
          Cu + AgNO3 ---> CuNO3 + Ag
4. Double Replacement (DR) or Ionic – ionic
  compounds swap partners/pairings

 General Form: AB + XY ---> AY + XB

 Examples: NaCl + AgNO3 ---> NaNO3 + AgCl

         Ba(OH)2 + NaBr --> BaBr2 + 2NaOH

     (NH4)2CO3 + CaCl2 --> 2NH4Cl + CaCO3

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