CHAPTER 7 CHEMICAL REACTIONS by malj

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									    CHAPTER 8
CHEMICAL REACTIONS
 LEARNING THE PATTERNS OF
   CHEMICAL REACTIONS
           INTRODUCTION
Section 8.1 Describing Chemical Change
   A. What is a CHEMICAL EQUATION?



   B. Why must an equation be balanced?
           INTRODUCTION
Section 8.1 Describing Chemical Change
   A. What is a CHEMICAL EQUATION?
     • A chemical sentence that describes
       chemical changes.
   B. Why must an equation be balanced?
     • to obey the law of conservation of mass
     • mass of reactants must equal mass of
       products
 C. 5 TYPES OF CHEMICAL
        REACTIONS
1. Combination (synthesis)
         A + B  AB
  2 reactants                  1 Product
  (each just 1 element)       (a compound)
  (monatomic or diatomic)
  Example:
     2H2 +      O2           2H2O
  C. 5 TYPES OF CHEMICAL
         REACTIONS
1. Combination (synthesis)
    A + B  AB
2. Decomposition
           AB  A + B
  1reactant             2 Products
  (a compound)        (each just elements)
 C. 5 TYPES OF CHEMICAL
        REACTIONS
3. Single Replacement
   A + BC  AC + B
  (A = metal) [metal, A, bonds with anion C]


   X + YZ YX + Z
  (X = nonmetal) [nonmetal, X, bonds with cation Y]
   C. 5 TYPES OF CHEMICAL
          REACTIONS
4. Double Replacement
        AB + CD  AD + CB
 CATION FROM ONE COMPOUND
  REPLACES THE CATION FROM THE
  OTHERAND THE ANION
 FROM ONE WILL
 REPLACE THE ANION
 FROM THE OTHER.
   C. 5 TYPES OF CHEMICAL
          REACTIONS
5. COMBUSTION (burning a hydrocarbon)
  – CXHY + O2  XCO2 + y/2 H2O

  Combustion of Propane:
  C3H8 + 5 O2  3 CO2 + 4 H2O
  These are all examples of COMPLETE combustion
    C. 5 TYPES OF CHEMICAL
           REACTIONS
5. COMBUSTION, continued
During COMPLETE combustion, there
  is enough oxygen to completely burn
  off all the fuel – the product is CO2.
During INCOMPLETE combustion, CO
  is produced instead, since there is not
  enough oxygen available.
   CHEMICAL EQUATIONS
D. Define REACTANTS -
  – starting substances
E. Define PRODUCTS -
  – ending substances
• Reactants  products
• “Reactants yield products”
                Table 8.1
        Symbols Used in Equations
      Use your textbook, page 206, to write the
      symbols for the following words/phrases
  •   yields                           •   solids
  •   precipitate is made              •   liquids
  •   a gas is produced                •   gases
  •   heat is being applied            •   aqueous
  •   a catalyst is used               •   heat
  •   a reversible reaction
It would be in your best interest to commit these symbols
and their meanings to memory.
              DEFINITIONS
G. What is a skeleton equation?
  – not balanced yet
H. What is a catalyst?
  – a substance that speeds up a
    reaction without being used up.
            Practice Problems
• Write a skeleton equation for each of these
  chemical reactions
  1. Aluminum metal reacts with oxygen in the air to form
     aluminum oxide.
  2. When solid mercury (II) sulfide is heated with oxygen,
     liquid mercury metal and gaseous sulfur dioxide are
     produced
  3. Oxygen gas can be made by heating potassium chlorate
     in the presence of the catalyst manganese dioxide.
     Potassium chloride is left as a solid residue..
            Practice Problems
• Write a skeleton equation for each of these
  chemical reactions
  1. Aluminum metal reacts with oxygen in the air to form
     aluminum oxide.
            Practice Problems
• Write a skeleton equation for each of these
  chemical reactions
  1. Aluminum metal reacts with oxygen in the air to form
     aluminum oxide.
            Practice Problems
• Write a skeleton equation for each of these
  chemical reactions
  2. When solid mercury (II) sulfide is heated with oxygen,
     liquid mercury metal and gaseous sulfur dioxide are
     produced
            Practice Problems
• Write a skeleton equation for each of these
  chemical reactions
  2. When solid mercury (II) sulfide is heated with oxygen,
     liquid mercury metal and gaseous sulfur dioxide are
     produced
            Practice Problems
• Write a skeleton equation for each of these
  chemical reactions
  3. Oxygen gas can be made by heating potassium chlorate
     in the presence of the catalyst manganese dioxide.
     Potassium chloride is left as a solid residue..
            Practice Problems
• Write a skeleton equation for each of these
  chemical reactions
  3. Oxygen gas can be made by heating potassium chlorate
     in the presence of the catalyst manganese dioxide.
     Potassium chloride is left as a solid residue..
• Write sentences that completely describe
  each of the chemical reactions shown in
  these skeleton equations.
  – KOH(aq) + H2SO4 (aq)  H2O(l) + K2SO4(aq)
  – Na(s) + H2O(l)  NaOH(aq) + H2(g)
• Write sentences that completely describe
  each of the chemical reactions shown in
  these skeleton equations.
  – KOH(aq) + H2SO4 (aq)  H2O(l) + K2SO4(aq)
  When potassium hydroxide, in aqueous solution combines with
    aqueous sulfuric acid, the result is liquid water and a
    potassium sulfate solution.

  – Na(s) + H2O(l)  NaOH(aq) + H2(g)
• Write sentences that completely describe each
  of the chemical reactions shown in these
  skeleton equations.
  – KOH(aq) + H2SO4 (aq)  H2O(l) + K2SO4(aq)
  When potassium hydroxide, in aqueous solution combines with
    aqueous sulfuric acid, the result is liquid water and a potassium
    sulfate solution.

  – Na(s) + H2O(l)  NaOH(aq) + H2(g)
  Solid sodium in liquid water yeilds a solution of sodium
    hydroxide and hydrogen bubbles.
        Balancing equations
• Remember, in a chemical reaction, atoms
  are not created or destroyed, but simply
  rearranged.
• In every balanced equation, each side of
  the equation has the same number of
  atoms of each element.
     Rules for Balancing Equations
                     from pg. 208-209

• 1. Determine the correct     • 3. Count the number
  formulas for all the           of atoms of each
  reactants and products in      element in the
  the reaction.
                                 reactants and products.
• 2. Write the formulas for
  the reactants on the left    • 4. If a polyatomic ion
  and the formulas for the       appearing unchanged
  products on the right with     on both sides of the
  an arrow in between. If        equation is counted as
  two or more reactants or       a single unit.
  products, separate them
  with a + sign
              Rules Con’t
• 5. Balance the        • CHECK EACH
  elements one at a       ATOM OR
  time using              POLYATOMIC ION
  coefficients. NEVER     TO BE SURE THAT
  CHANGE A                THE EQUATION IS
  SUBSCRIPT TO            BALANCED
  BALANCE AN            • 6. MAKE SURE
  EQUATION!!!!!           COEFFICIENT
                          RATIO IS LOWEST
                          POSSIBLE RATIO.
   PRACTICE BALANCING
• PROBLEM 3 PG 209   • PROBLEM 4 PG 209

								
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