Chapter 7Chemical Reactions

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Chapter 7Chemical Reactions

• Dr. Ellen Wilson
• CHE-1000-58793
• Fall 2007

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What is a chemical reaction?

• A change of one or more substances into
• different substances

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How Do We Know a Chemical Reaction Has Occurred?
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Precipitation is Evidence of a Chemical Reaction
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Color Change is Evidence of a Chemical Reaction

• Pb(NO3)2(aq) 2NaI(aq) ?PbI2(s) 2NaNO3(aq)

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Color Change is Evidence of a Chemical Reaction
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Gas Evolution is Evidence of a Chemical Reaction
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This is the Same Reaction that Makes a Baking
Soda Volcano!
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Gas Evolution is Evidence of a Chemical Reaction
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Heat Transfer is Evidence of a Chemical Reaction

• Reactions can be either endothermic or exothermic

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Endothermic Reactions Use Heat
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Endothermic Reaction Demo
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Exothermic Reactions Give Off Heat
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Exothermic Reactions Give Off Heat
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Exothermic Reaction Demo
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• Light Emission is Evidence of a Chemical Reaction

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The Color of a Firework Depends on the Salt Added
to It
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The Color of a Firework Depends on the Salt Added
to It
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Categories of Chemical Reactions
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Synthesis

• A B ? C
• Ca(s) Cl2(g) ? CaCl2(s)

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Decomposition

• A ? B C
• 2NaN3(s) ? 2Na(s) 3N2(g)

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Single-Displacement

• one element replaces another
• 2Al(s) Fe2O3(s) ? Al2O3(s) 2Fe(s)

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Double-Displacement

• two elements exchange places
• Pb(NO3)2(aq) 2NaI(aq) ?PbI2(s) 2NaNO3(aq)

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Which Type of Reaction?
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Which Type of Reaction?
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Which Type of Reaction?
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Which Type of Reaction?
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Chemical Equation

• A chemical reaction is represented by a balanced,
  chemical equation

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What Does a Chemical Equation Look Like?
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Synthesis

• A B ? C
• Ca(s) Cl2(g) ? CaCl2(s)

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Decomposition

• A ? B C
• 2NaN3(s) ? 2Na(s) 3N2(g)

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Single-Displacement

• one element replaces another
• 2Al(s) Fe2O3(s) ? Al2O3(s) 2Fe(s)

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Double-Displacement

• two elements exchange places
• Pb(NO3)2(aq) 2NaI(aq) ?PbI2(s) 2NaNO3(aq)

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Chemical Equations

• What does a chemical equation tell us?
• CH4(g) 2O2(g) ? CO2(g) 2H2O(g)
• Atoms Molecules
• Moles of atoms/molecules
• Avogadros number of atoms/molecules
• Grams of substances

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Balancing Chemical Equations

• A chemical equation MUST be balanced in order to
  be
• of any use to us

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Balancing Chemical Equations

• Tips and Hints
• write the unbalanced equation, compare numbers of
  like atoms on each side
• start with the most complicated molecule
• use coefficients so that the same number of each
  type of atom appears on both sides of the
  equation
• do not change the subscripts of any of the
  reactants or products

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Unbalanced Chemical Equation

• C2H5OH(l) O2(g) ? CO2(g) H2O(g)

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Balancing Chemical Equations

• C2H5OH(l) O2(g) ? 2CO2(g) H2O(g)

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Balancing Chemical Equations

• C2H5OH(l) O2(g) ? 2CO2(g) 3 H2O(g)

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Balancing Chemical Equations

• C2H5OH(l) 3O2(g) ? 2CO2(g) 3 H2O(g)

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Unbalanced Chemical Equation

• NH3(g) CuO(s) ? N2(g) Cu(s) H2O(g)

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Balancing Chemical Equations

• 2NH3(g) CuO(s) ? N2(g) Cu(s) H2O(g)

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Balancing Chemical Equations

• 2NH3(g) CuO(s) ? N2(g) Cu(s) 3H2O(g)

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Balancing Chemical Equations

• 2NH3(g) 3CuO(s) ? N2(g) Cu(s) 3H2O(g)

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Balancing Chemical Equations

• 2NH3(g) 3CuO(s) ? N2(g) 3Cu(s) 3H2O(g)

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Unbalanced Chemical Equation

• NH3(g) O2(g) ? NO(g) H2O(g)

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Balancing Chemical Equations

• 2NH3(g) O2(g) ? NO(g) 3H2O(g)

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Balancing Chemical Equations

• 2NH3(g) O2(g) ? 2NO(g) 3H2O(g)

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Balancing Chemical Equations

• 2NH3(g) 5/2O2(g) ? 2NO(g) 3H2O(g)

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Balancing Chemical Equations

• Never leave a fraction in a chemical equation
  multiply by some number to make the fraction a
  whole number

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Balancing Chemical Equations

• 4NH3(g) 5O2(g) ? 4NO(g) 6H2O(g)

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Types of Chemical Reactions
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What is an Aqueous Solution?
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• What Does It Mean to Dissolve?

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What is Dissociation?
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Which Compounds are Soluble?
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Which are Insoluble?
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What is a Precipitation Reaction?
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What is a Precipitation Reaction?

• A precipitation reaction
• is the combination of two
• aqueous (aq) solutions
• that results in the formation
• of an insoluble (s) product

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What is a Precipitation Reaction?
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What is a Precipitation Reaction?

• A precipitation reaction is a
• double-displacement reaction

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Examples of Precipitation Reactions
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Balanced Chemical Equation
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Examples of Precipitation Reactions
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Balanced Chemical Equation
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Examples of Precipitation Reactions
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Balanced Chemical Equation
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Examples of Precipitation Reactions
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Balanced Chemical Equation
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Examples of Precipitation Reactions
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Balanced Chemical Equation
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Types of Chemical Equations
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Molecular Equation
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Complete and Net Ionic Equations
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Molecular Equation
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Complete and Net Ionic Equations
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Molecular Equation
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Complete and Net Ionic Equations
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Molecular Equation
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Complete and Net Ionic Equations
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What is an Acid-Base Reaction?
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What is an Acid?

• From Chapter 5, a compound that contains
• hydrogen plus one nonmetal or
• hydrogen plus an oxygen-containing polyatomic
  anion
• A compound that dissociates in water to give a
  hydrogen ion and an anion

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What is an Acid?
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Acids
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Some Common Acids
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What is a Base?

• A compound that contains a
• metal plus a hydroxide group
• A compound that dissociates in water to give a
  metal cation and a hydroxide anion

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What Is A Base?
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Bases
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Some Common Bases
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Examples of Acid-Base Reactions
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Examples of Acid-Base Reactions
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Examples of Acid-Base Reactions