Chemical Reactions

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Chemical Reactions

• Chapter 3
• 3.1-3.6

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Learning Objectives

• Students understand
• The significance and uses of balanced chemical
  equations
• The nature and characteristics of chemical
  equilibrium
• The nature of ionic substances dissolved in water
• Oxidation-reduction reactions and the three types
  of exchange reactions
• Acid-base reactions involve the transfer of
  hydrogen ions

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Learning Objectives

• Students will be able to
• Balance chemical equations
• Predict solubility and species present
• Recognize common types of reactions and predict
  products
• Know names and formulas of common acids bases
• Write a net ionic equation
• Determine oxidation numbers

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3.1 Chemical Equations

• the reactants are written to the left and the
  products are written to the right of the arrow
• s, g, l, aq indicate the states of matter
• coefficients are used to show the relative
  amounts
• the law of conservation of matter (Antoine
  Lavoisier)

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Chemical Equations

• balanced equations vs. skeleton equations
• relationship between amounts is stoichiometry
• stoichiometric coefficients indicate number of
  atoms, molecules, formula units, or moles

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3.2 Balancing

• Formulas for reactants and products have to be
  written correctly
• Subscripts cannot be changed to balance

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Balancing Combustion

• Step 1 write correct formulas for reactants and
  products
• Step 2 balance the carbon atoms
• Step 3 balance the hydrogen atoms
• Step 4 balance the oxygen atoms
• Step 5 verify atoms are balanced

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Combustion Reactions

• Complete oxidation of an organic compound to
  yield CO2 and H2O
• C2H4(g) 3O2(g) ? 2CO2(g) 2H2O(l)
• Nonmetallic hydrides combine with oxygen to form
  oxides and water
• SiH4(g) 2O2(g) ? SiO2(s) 2H2O(l)
• Nonmetallic sulfides combine with oxygen to form
  sulfur dioxide and oxides
• CS2(s) 3O2(g) ? CO2(g) 2SO2(g)

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3.3 Chemical Equilibrium

• Reactions are reversible, and many reactions lead
  to incomplete conversion of reactants to
  products.
• Chemical equilibrium is when no macroscopic
  change is observed.
• Dynamic equilibrium indicates the forward and
  reverse reactions are occurring at equal rates.

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Chemical Equilibrium

• Depending upon different factors, product-favored
  reactions are reactions in which reactants are
  largely converted to products at equilibrium.
• Reactant-favored reactions mean that at
  equilibrium only a small amount of reactants have
  been converted to products.

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3.4 Reactions in Aqueous Solution

• Another name for a solution is a homogeneous
  mixture.
• solute and solvent
• Substance dissolved in water are called aqueous
  solutions.
• Polarity of water creates an attraction for ions.
• Water molecules surround each ion in the
  dissolved substance.

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Reactions in Aqueous Solutions

• Four major categories of chemical reactions
• synthesis
• decomposition
• oxidation-reduction
• acid-base reactions

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Ions and Molecules

• Compounds that conduct electricity in aqueous
  solution are called electrolytes.
• All ionic compounds that are soluble in water are
  electrolytes.
• Strong electrolytes completely ionize in
  solution. (such as salt)
• Weak electrolytes only partially dissociate.
  (such as acetic acid)
• Nonelectrolytes dissolve in water but dont
  ionize. (such as sugar)
• Most molecular compounds that dissolve in water
  are nonelectrolytes.

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Solubility of Ionic Compounds in Water

• Although many ionic compounds dissolve
  completely, some dissolve only to a small extent
  and some are essentially insoluble.
• Solubility rules on page 108

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3.5 Precipitation Reactions

• precipitation reactions form insoluble products
  (precipitate)
• lead nitrate and potassium iodide
• products can be predicted using solubility rules

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Net Ionic Equations

• net ionic equations leave out the spectators
• Strong acids, strong bases, and soluble salts
  exist as ions in solution
• All other species are represented by their
  complete formulas (weak acids, weak bases,
  insoluble salts, etc.)

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Net Ionic Equations

• Write a complete, balanced equation and indicate
  the state of each substance.
• Rewrite the whole equation, ionizing species
  where appropriate (only aq)
• Cross off spectators
• Mass and charge balance!

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Practice Problems

• Write a balanced net ionic equation for each of
  the following reactions
• AlCl3 Na3PO4? AlPO4 NaCl
• Solutions of iron (III) chloride and potassium
  hydroxide give iron (III) hydroxide and potassium
  chloride when combined.
• Solutions of lead (II) nitrate and potassium
  chloride give lead (II) chloride and potassium
  nitrate when combined.

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Practice Problems

• Write balanced, net ionic equations for each of
  these reactions that occur between aqueous
  solutions.
• CaCl2 Na3PO4
• Iron(III) chloride and potassium iodide
• Lead(II) nitrate and potassium chloride

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3.6 Acids and Bases

• Properties of acids and bases
• Reactivity
• Taste
• indicators
• Common Acids and Bases p. 115

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Arrhenius Acids and Bases

• Focuses on formation of hydrogen and hydroxide
  ions in solution
• An acid, when dissolved in water, increases the
  concentration of hydrogen ions, H, in solution.
• A base, when dissolved in water, increases the
  concentration of hydroxide ions, OH-, in solution.

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Arrhenius Acids and Bases

• The reaction of an acid and a base produces a
  salt and water. Acid-base reactions were
  logically described as resulting from the
  combination of H and OH- to form water.
• Proposed that acid strength was related to the
  extent to which the acid ionized strong vs.
  weak acids and bases

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Brønsted-Lowry Acids and Bases

• Viewed acids and bases in terms of the transfer
  of a proton (H)
• Described in terms of equilibria
• An acid is a proton-donor.
• A base is a proton-acceptor.
• An acid-base reaction involves the transfer of a
  proton from an acid to a base to form a new acid
  and a new base.

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Brønsted-Lowry Acids and Bases

• Amphiprotic species that can function as either
  an acid or a base

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Brønsted-Lowry Acids and Bases

• Acids capable of transferring two or more H ions
  react with water in multiple steps. Different
  steps may favor different sides of equilibrium.
• Sulfuric acid is capable of transferring two
  protons. The first step is product-favored but
  the second step is reactant-favored.

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Practice Problem

• Write a balanced equation for the reaction that
  occurs when H3PO4 donates a proton to water to
  form the dihydrogen phosphate ion.
• Write a net ionic equation showing the dihydrogen
  phosphate ion acting as an acid in a reaction
  with water.

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Reactions of Acids and Bases

• Acids and bases usually react to produce a salt
  (any ionic compound whose cation comes from a
  base and whose anion comes from an acid) and
  water.
• Neutralization Reactions

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Oxides of Nonmetals and Metals

• Oxides of nonmetals such as CO2, SO2, SO3, and
  NO2 that react with water to produce an acidic
  solution are called acidic oxides.
• Oxides of metals are called basic oxides because
  they produce basic solutions in water, such as
  CaO.

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Oxides of Nonmetals and Metals

• metal oxide nonmetal oxide ? salt
• 6CaO(s) P4O10(s) ? 2Ca3(PO4)2(s)

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Homework

• After reading Sections 3.1-3.6, you should be
  able to do the following
• P. 137b-c (15-16, 19-20, 32-33, 37-40)