Chemical Reactions PAK 6

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Chemical Reactions PAK 6
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Introduction

• Chemical reactions occur when bonds between the
  valence electrons of atoms are formed or broken
• Chemical reactions involve changes in matter, the
  making of new materials with new properties, and
  energy changes.
• Symbols represent elements
• Formulas describe compounds
• Equations describe a chemical reaction

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Parts of an Equation

• Reactants ? Products
• State of Matter Symbols
• Solid (s)
• Liquid (l)
• Gas (g)
• Aqueous Solution (aq)

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Conservation of Matter

• Balancing equations demonstrates the
• Law of Conservation of Matter
• Matter cannot be created or destroyed.
• All matter at the start of a reaction must be
  present at the end of a reaction.

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Subscripts vs. Coefficients

• Subscripts balance a formula
• Coefficients balance an equation

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Types of Reactions

• There are five types of chemical reactions we
  will talk about
• Synthesis or Combination
• Decomposition
• Single Replacement
• Double Replacement
• Combustion
• You need to be able to identify the type of
  reaction and predict the product(s)

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1. Synthesis reactions

• two substances combine to form a single compound
  
• reactant reactant ? 1 product
• or
• A B ? AB
• Example 2H2 O2 ? 2H2O
• Example C O2 ? CO2

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Synthesis Reactions
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Practice

• Sodium metal reacts with chlorine gas
• Na(s) Cl2(g) ? NaCl
• 2Na(s) Cl2(g) ? 2NaCl
• Solid Magnesium reacts with fluorine gas
• Mg(s) F2(g) ? MgF2
• Aluminum metal reacts with fluorine gas
• Al(s) F2(g) ? AlF3
• 2Al(s) 3F2(g) ? 2AlF3

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2. Decomposition Reactions

• One compound breaks up into elements or simpler
  compounds
• 1 Reactant ? Product Product
• or
• AB ? A B
• Example 2 H2O ? 2H2 O2
• Example 2 HgO ? 2Hg O2

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Decomposition Reactions
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Practice

• Solid Lead (II) oxide decomposes
• PbO(s) ?
• 2PbO(s) ? 2Pb O2
• Aluminum nitride decomposes
• AlN ?
• AlN ? Al N2
• 2AlN ? 2Al N2

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Practice

• N2(g) O2(g) ?
• N2(g) O2(g) ? 2NO
• NH3 ?
• 2NH3 ? N2 3H2
• Co(s) S(s) ?
• 2Co(s) 3S(s) ? Co2S3

Nitrogen monoxide
(make Co be 3)
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3. Single Replacement Reactions

• one element replaces another in a compound
• element compound? product product
• or
• A BC ? AC B
• (remember the cation always goes first!)
• Use the ACTIVITY SERIES to determine if reaction
  will occur.
• Example Cu AgNO3 ? Ag CuNO3
• Example 2Al 3CaO ? No Reaction

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Single Replacement Reactions
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Single Replacement Reactions

• Use the Activity Series
• Mg(s) ZnCl2(s) ?
• Mg(s) AgCl(s) ?
• Mg(s) LiCl(s) ?

Zn(s) MgCl2(s)
Ag(s) MgCl2(s)
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2
No Reaction
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4. Double Replacement Reactions

• The metals in the two compounds switch places
• Compound compound ? product product
• or
• AB CD ? CB AD
• Use SOLUBILITY RULES to find state of products
• Example CaF2(aq) H2SO4(aq) ? CaSO4(s)
  HF(aq)
• Example AgNO3(aq) KCl(aq) ? AgCl(s)
  KNO3(aq)

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Practice

• FeCl3(aq) NaOH(aq) ?
• FeCl3(aq) NaOH(aq) ? Fe(OH)3 NaCl
• FeCl3(aq) NaOH(aq) ? Fe(OH)3(s) NaCl
  (aq)
• FeCl3(aq) 3NaOH(aq) ? Fe(OH)3(s) 3NaCl
  (aq)
• H2SO4(aq) BaCl2(aq) ?
• H2SO4(aq) BaCl2(aq) ? HCl BaSO4
• H2SO4(aq) BaCl2(aq) ? HCl(aq) BaSO4(s)
• H2SO4(aq) BaCl2(aq) ? 2HCl(aq) BaSO4(s)

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5. Combustion Reactions

• Combustion reactions occur when something burns.
• Oxygen is always one of the reactants!
• CxHy O2 ? CO2 H2O

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Combustion

• Example
• C5H12 O2 ? CO2 H2O
• 
  
  
  
  
  
  
  
  
  
  
  
  

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Mixed Practice

• State the type, predict the products, and balance
  the following reactions.
• When Mrs. Bancroft approves your answers you may
  go!
• Pb(NO3)2 (aq) KI (aq)?
• C6H12 O2 ?
• Zn CuSO4 ?
• Li Br2 ?
• NaCl ?