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Chapter 11 Chemical Reactions_1_

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					                  Chapter 6
                 Chemical
                 Reactions
       Honors Chemistry
    Lane Tech College Prep

1
             Section 11.1
    Describing Chemical Reactions
    l   OBJECTIVES:
        –Describe how to write a
         word equation.


2
             Section 11.1
    Describing Chemical Reactions
    l   OBJECTIVES:
        –Describe how to write a
         skeleton equation.


3
             Section 11.1
    Describing Chemical Reactions
    l   OBJECTIVES:
        –Describe the steps for
         writing a balanced
         chemical equation.

4
      Describing a Chemical Reaction
Indications of a Chemical Reaction

  – Evolution of heat, light, and/or sound

  – Production of a gas

  – Formation of a precipitate

  – Color change (not blend)


  5
    All chemical reactions have:
1. Reactants = the substances you
   start with
2. Products = the substances you
   end up with
-The reactants turn
into the products

Reactants à
Products
6
                - Page 321


    Products
    Reactants




7
           In a chemical reaction
l    Atoms aren’t created or destroyed (according
     to the Law of Conservation of Mass)




    8
CH4 + 2 O2 à CO2 + 2 H2O




    Reactants    Products
     1 C atom     1 C atom
     4 H atoms    4 H atoms
     4 O atoms    4 O atoms

9
 l   A reaction can be described several
     ways:
 #1. In a sentence- all words
   Copper reacts with chlorine to form
      copper (II) chloride.


 #2. In a word    equation- some symbols
   are used
 Copper + chlorine ® copper (II) chloride

10
      #3. The Skeleton Equation
l    Uses formulas and symbols to
     describe a reaction
     –but doesn’t indicate how many;
      this means they are NOT
      balanced
l    All chemical equations are a
     description of the reaction.
    11
             Types of Equations
WORD EQUATION: an equation in which the reactants and
 products in a chemical reaction are represented by words.
  methane    +   oxygen            carbon dioxide + water
SKELETON EQUATION: an equation in which the reactants
  and products in a chemical reaction are represented by
  their symbols or formulas (DOES NOT INDICTATE
  RELATIVE AMOUNTS OF REACTANT AND PRODUCTS).
              CH4 + O2                 CO2 + H2O

CHEMICAL EQUATION: a balanced formula equation.
             CH4   + 2 O2            CO2    +   2H2O

  12
          Symbols in equations?
l   the arrow (→) separates the reactants
    from the products (arrow points to products)
    –Read as: “reacts to produce” or yields
l    “+” sign = “and”
l    (s) after the formula = solid: Fe(s)
l    (g) after the formula = gas: CO2(g)
l    (l) after the formula = liquid: H2O(l)
    13
     Symbols used in equations
l   (aq) after the formula = dissolved
    in water, an aqueous solution:
    NaCl(aq) is a salt water solution




14
                                                          H
        (s ) Showing Phases in 2 SO
    M gO Chemical Equations 4 (aq
                                    )
          N H 3(l)       CH (g
                             4 )
•   Solid Phase – the substance is relatively rigid and has a definite
    volume and shape. EX: NaCl(s)


•   Liquid Phase – the substance has a definite volume, but is able to
    change shape by flowing. EX: H2O (l)


•   Gaseous Phase – the substance has no definite volume or shape,
    and it shows little response to gravity. Cl2(g)

•   Aqueous Phase – the substance is dissolved in water. EX: KOH (aq)

    15
       Remember the Diatomic
           Molecules!!

       l   HONClBrIF!!

…Just like two headed   H H
monsters cannot go
anywhere alone!!


 16
     Write a skeleton equation for:
1.   Solid iron (III) sulfide reacts with
     gaseous hydrogen chloride to form
     solid iron (III) chloride and
     hydrogen sulfide gas.
2.   Nitric acid dissolved in water reacts
     with solid sodium carbonate to form
     liquid water, carbon dioxide gas and
     sodium nitrate dissolved in water.

17
     Now, read these equations:
Fe(s) + O2(g) ® Fe2O3(s)

Cu(s) + AgNO3(aq) ® Ag(s) + Cu(NO3)2(aq)

NO2(g)           N2(g) + O2(g)



18
#4. Balanced Chemical Equations
l    Atoms can’t be created or destroyed
     in an ordinary reaction:
      –All the atoms we start with we must
       end up with (meaning: balanced!)
l    A balanced equation has the same
     number of each element on both
     sides of the equation.
    19
          Rules for balancing:
1)   Assemble the correct formulas for all the
     reactants and products, using “+” and “→”
2)   Set up the RIP Chart
3)   Count the number of atoms of each type
     appearing on both sides
4)   Balance the elements one at a time by
     adding coefficients (the numbers in front)
     where you need more – hint: save balancing
     the H and O until LAST!
5)   Double-Check to make sure it is balanced.
20
Catalyst: Write a balanced equation for:
1.   Solid carbon reacts with gaseous
     oxygen to form gaseous carbon
     dioxide.
2.   Solid zinc is added to an aqueous
     solution containing dissolved
     hydrogen chloride to produce
     gaseous hydrogen that bubbles out
     of the solution and zinc chloride
     that remains dissolved in the water.
21
     11/28 - Today’s Objectives:
 I CAN…
 lIdentify oxides and peroxides
 lKnow what a catalyst is and where to
 write it in a chemical equation.
 lWrite a skeleton equation from a
 sentence description of a chemical
 reaction.
 lBalance chemical equations using the
 RIP method.
22
     11/28 – Announcements / HW
 l   Quiz Friday on writing and balancing
     chemical equations.
 l   PowerPoint will be posted today.
 l   Tutoring today in Rm. 115 and
     tomorrow in Rm. 243!
 l   Participation grade pre-test (for me)
     will be given tomorrow.
 l   HW: Ch. 6 #’s 13, 14, 15, 18, 37
23
l    Never change a subscript to balance an
     equation (You can only change coefficients)
      – If you change the subscript (formula) you
        are describing a different chemical.
      – H2O is a different compound than H2O2
l    Never put a coefficient in the middle of a
     formula; they must go only in the front
          2NaCl is okay, but Na2Cl is not.
    24
     Classify the following as an oxide or
                  a peroxide:
 l    Na2O2
 l    MgO2
 l    BeO
 l    K 2O
 l    (NH4)2O2



25
     Now, read these equations:
Fe(s) + O2(g) ® Fe2O3(s)

Cu(s) + AgNO3(aq) ® Ag(s) + Cu(NO3)2(aq)

NO2(g)           N2(g) + O2(g)



26
          What is a catalyst?
l     A substance that speeds up a
     reaction, without being
     changed or used up by the
     reaction.
l     Enzymes are biological or
     protein catalysts in your body.
    27
     Practice Balancing Examples
l _AgNO3
  2          + _Cu ® _Cu(NO3)2 + 2
                                 _Ag

l _Mg
  3       + _N2 ® _Mg3N2

l _P
  4      + _O2 ® _P4O10
           5


l _Na
  2       + _H2O ® _H2 + _NaOH
            2            2


l    _CH4 + _O2 ® _CO2 + 2 2O
            2            _H
    28
     Symbols used in equations
■         double arrow indicates a
  reversible reaction (more later)
■                       shows that
  heat is supplied to the reaction
■           is used to indicate a
  catalyst is supplied (in this case,
  platinum is the catalyst)
29
     Week 11 HW: 11/26-11/30
 Date              Assignment
 Monday 11/26      Internet Balancing Activity Wksht
 Tuesday 11/27     Equation Writing Practice Wksht
 Wednesday 11/28   Ch. 6 #’s 13, 14, 15, 18, 37
 Thursday 11/39      [Go to tutoring in Rm. 243 for extra help today]
                   Reading and Notes TBA
 Friday 11/30        [Balancing and Writing Equations Quiz Today!]
                   HW TBA




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