FACTORS (driving forces) THAT CAUSE REACTION TO OCCUR:

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FACTORS (driving forces) THAT CAUSE REACTION TO
OCCUR

• Formation of a solid
• Formation of water
• Transfer of electrons
• Formation of a gas
• Review polyatomic ions these will be needed to
  write chemical equations in this chapter.

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Precipitation Reactions in which solid forms

• One of the reaction products is insoluble
• Pb(NO3)2(aq) 2 KI(aq) ? 2 KNO3(aq)
  PbI2(s)
• Many reactions are done by mixing aqueous
  solutions of electrolytes (solutions containing
  ions) together.
• - When this is done, often a reaction will take
  place as a result of the cations and anions in
  the two solutions exchanging.
• - If the ion exchange results in forming a
  compound that is insoluble in water, it will
  come out of solution as a precipitate. The
  reaction is known as a precipitation reaction.

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No Precipitate Formation Results in No Reaction
Occurring
KI(aq) NaCl(aq) ? KCl(aq) NaI(aq) If all ions
are still present, then there is no reaction
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Solubility Rules See Table 7.1

• Most (NO3-) salts are soluble.
• Most salts of Na, K, and NH4 are soluble.
• Most chloride salts are soluble. Exceptions
  AgCl, PbCl2, and Hg2Cl2
• Most sulfate salts are soluble. Exceptions
  BaSO4, PbSO4, and CaSO4
• Most hydroxide compounds are only slightly
  soluble. Exceptions NaOH and KOH. Ba(OH)2 and
  Ca(OH)2 are only slightly soluble.
• Most sulfides (S2-), carbonate (CO32-), and
  phosphate (PO43-) salts are only slightly
  soluble.
• note slightly soluble ? insoluble

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Process for Predicting the Products ofa
Precipitation Reaction

• Determine what ions are present in each aqueous
  reactant.
• Exchange the Ions as if a reaction occurred
• () ion from one reactant with (-) ion from
  another.
• Balance the charges of the newly combined ions to
  get a formula for each product.
• Balance the Equation
• count all of the atoms in the reactants and
  products and make sure the same number and kinds
  of atoms are in both reactants and products.
• Determine the Solubility of Each Product in
  Water
• use the Solubility Rules
• if a product is insoluble or slightly soluble, it
  will precipitate.
• if neither product will precipitate, there is no
  reaction.

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Example - When an aqueous solution of sodium
carbonate is added to an aqueous solution of
copper(II) chloride, a white solid forms

• Write the formulas of the reactants
• Na2CO3(aq) CuCl2(aq) ?
• Determine the ions present when each reactant
  dissociates
• (Na CO32-) (Cu2 Cl-) ?
• Exchange the Ions
• (Na CO32-) (Cu2 Cl-) ? (Na Cl-)
  (Cu2 CO32-)
• Write the formulas of the products
• cross charges and reduce
• Na2CO3(aq) CuCl2(aq) ? NaCl CuCO3
• Balance the Equation
• Na2CO3(aq) CuCl2(aq) ? 2 NaCl CuCO3
• Determine the solubility of each product
• NaCl is soluble and CuCO3 is insoluble
• Write an (s) after the insoluble products and a
  (aq) after the soluble products
• Na2CO3(aq) CuCl2(aq) ? 2 NaCl(aq) CuCO3(s)

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Additional Examples

• In the following reaction a white solid forms,
  identify the solid and write the balanced
  equation
• Ba(NO3)2(aq) Na2SO4(aq)
• 2. In the following reaction a yellow solid
  forms, identify the solid and write the balanced
  equation
• Pb(NO3)2(aq) KI(aq)
• 3. Predict what will happen when the following
  solutions are mixed and write the balanced
  equation
• Ba(NO3)2(aq) K3PO4(aq)
• Predict what will happen when the following
  solutions are mixed and write the balanced
  equation
• Na2SO4(aq) KCl(aq)

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Reactions in Aqueous Solutions

• Equations which describe the chemicals put into
  the water and the product molecules are called
  molecular equations
• 2 KOH(aq) Mg(NO3)2(aq) ?2 KNO3(aq) Mg(OH)2(s)
• Equations which describe the actual dissolved
  species are called complete ionic equations
• aqueous electrolytes are written as ions
• soluble salts, strong acids, strong bases
• insoluble substances and nonelectrolytes are
  written as molecules
• solids, liquids and gases are not dissolved,
  therefore they are written as molecules
• 2K1(aq) 2OH-1(aq) Mg2(aq) 2NO3-1(aq)
  2K1(aq) 2NO3-1(aq) Mg(OH)2(s)
• Net Ionic Equation 2OH-1(aq) Mg2(aq)
  Mg(OH)2(s)

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Conventional (Molecular) Equation
HCl(aq) NaOH(aq) H2O(l)
NaCl(aq)
Pros Actual starting materials Easier to balance
equations Easier for stoichiometry problems
Cons Does not accurately describe rxn, reactants
or products Less useful with equilibrium problems
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Total Ionic Equation
H(aq) Cl-(aq) Na(aq) OH-(aq)
H2O(l) Na(aq) Cl-(aq)
Pros Accurately describes rxn, reactants and
products
Cons Cannot determine starting material Less
useful with stoichiometry Difficult to balance
equation Spectator ions on each side Long
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Net Ionic Equation
H(aq) OH-(aq) H2O(l)
Pros Indicates chemical change Concise Same as
total ionic, but w/o spectator ions
Cons Cannot determine starting material
The net ionic equation tells the chemistry that
occurs, and nothing else (that is its purpose)
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Writing Net Ionic Equations
Conventional (Molecular) Equation
HCl(aq) NaOH(aq) H2O(l)
NaCl(aq)
Total Ionic Equation
H(aq) Cl-(aq) Na(aq) OH-(aq)
H2O(l) Na(aq) Cl-(aq)
Net Ionic Equation
H(aq) OH-(aq) H2O(l)
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Writing Net Ionic Equations
Conventional (Molecular) Equation
Na2SO4(aq) Pb(NO3)2(aq) PbSO4(s) 2
NaNO3(aq)
Total Ionic Equation
2 Na(aq) SO42-(aq) Pb2(aq) 2 NO3-(aq)
PbSO4(s) 2 Na(aq) SO42-(aq)
Net Ionic Equation
SO42-(aq) Pb2(aq) PbSO4(s)
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Reaction that form WaterAcids and Bases
Everyday acids and bases we use Acids Bases Sof
t Drinks Detergents Fruits Drain-cleaning
products
Where have we heard and used an acid or base
in this class?
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What Are Acids and Bases?
Every aqueous solution has mostly water
molecules, but also has both hydronium ions (H)
and hydroxide ions (OH-)
H2O
H2O
H
OH-
H2O
H2O
H2O
An acidic solution is one where there are more
hydronium ions (H) than hydroxide ions (OH-)
H
H2O
H
OH-
H2O
H
H2O
A basic solution is one where there are more
hydroxide ions (OH-) than hydronium ions (H)
H2O
OH-
H2O
H
OH-
H2O
OH-
H2O
This is the Arrhenius theory
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Acidic, Basic, or Neutral?
Neutral H OH- Acidic H gt
OH- Basic OH- gt H or H lt OH-
H2O
H2O
H
OH-
H2O
H2O
H2O
H
H2O
H
OH-
H2O
H
H2O
H2O
OH-
H2O
H
OH-
H2O
OH-
H2O
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Acid, Base Strength
Vinegar and sulfuric acid are both acids One we
consume, one will kill us Baking soda and drain
cleaners are both bases One we put in the
refrigerator, the other will make us sick Acids
and bases come in a variety of strengths - some
are strong and others are weak
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Examples of Strong Acids
Recognize the following strong acids Nitric
acid (HNO3) Sulfuric acid (H2SO4) Hydrochloric
acid (HCl) Hydrobromic acid (HBr) Hydroiodic acid
(HI) Chloric acid (HClO3) Perchloric acid (HClO4)
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Strong Acid very conductive solution as it
ionizes
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Weak Acid (or base) barely lights up as there
are few ions in solution
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Example of Weak Acids

• Most organic acids (acetic, oxalic, citric, fatty
  acids)
• HF Hydrofluoric acid
• H2CO3 Carbonic acid (soda pop)
• H3PO4 Phosphoric acid (also in Coke)
• H3BO3 Boric acid (used in eye washes)

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Acid-Base Reactions

• Acid-Base reactions are also called
  neutralization reactions because the acid and
  base neutralize each others properties to form a
  salt and water.
• In the reaction of an acid with a base, the H
  from the acid combines with the OH-from the base
  to make water.
• The cation from the base combines with the anion
  from the acid to make the salt
• acid base ???salt water
• 2 HNO3(aq) Ca(OH)2(aq) ? Ca(NO3)2(aq) 2
  H2O(l)
• the net ionic equation for an Acid-Base reaction
  is
• H1(aq) OH-1(aq) ? H2O(l)
• as long as the salt that forms is soluble in water

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Oxidation/Reduction

• Atoms undergo changes in oxidation state.
• Atoms that lose electrons become oxidized and
  atoms that gain electrons become reduced.
• They always accompany each other
• 2Mg(s) O2 ? 2MgO(s)
• you cannot have one without the other

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Reactions of Metals with Nonmetals(Oxidation-Redu
ction)

• Metals react with nonmetals to form ionic
  compounds
• ionic compounds are solids at room temperature.
• The metal loses electrons and becomes a cation
• the metal undergoes oxidation.
• The nonmetal gains electrons and becomes an anion
• the nonmetal undergoes reduction.
• In the reaction, electrons are transferred from
  the metal to the nonmetal
• 2 Na(s) Cl2(g) ? 2 NaCl(s)

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Oxidation-Reduction Reactions

• Any reaction that has an element that is
  uncombined on one side and combined on the other
  is a redox reaction
• uncombined free element
• 2 CO O2 ? 2 CO2
• 2 N2O5 ? 4 NO2 O2
• 3 C Fe2O3 ? 3 CO 2 Fe
• Mg Cl2 ? MgCl2
• Any reaction where a cation changes charge is
  redox
• CuCl FeCl3 ? FeCl2 CuCl2
• SnCl2 F2 ? SnCl2F2

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Your Car Battery
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Rust is the result of an Oxidation/Reduction
Reaction
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Gas Evolving Reactions Reactions that form a gas

• Some reactions form a gas directly from the ion
  exchange
• K2S(aq) H2SO4(aq) ? K2SO4(aq) H2S(g)
• Other reactions form a gas by the decomposition
  of one of the ion exchange products into a gas
  and water
• K2SO3(aq) H2SO4(aq) ? K2SO4(aq) H2SO3(aq)
• H2SO3 ? H2O(l) SO2(g)

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Compounds that UndergoGas Evolving Reactions
Reactant Type Reacting With Ion Exchange Product Decom-pose? Gas Formed Example
metalnS, metal HS acid H2S no H2S K2S(aq) 2HCl(aq) ? 2KCl(aq) H2S(g)
metalnCO3, metal HCO3 acid H2CO3 yes CO2 K2CO3(aq) 2HCl(aq) ? 2KCl(aq) CO2(g) H2O(l)
metalnSO3 metal HSO3 acid H2SO3 yes SO2 K2SO3(aq) 2HCl(aq) ? 2KCl(aq) SO2(g) H2O(l)
(NH4)nanion base NH4OH yes NH3 KOH(aq) NH4Cl(aq) ? KCl(aq) NH3(g) H2O(l)
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Types of Chemical Reactions1. Combination or
Synthesis Reaction
Two or more elements combine to form one
molecule A X AX 2 Cu
S Cu2S 2 CO O2 2 CO2 2 Mg
O2 2 MgO HgI2 2 KI K2HgI4
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2. Decomposition Reactions
One compound breaks down into simpler
substances AX A X 2 H2O 2 H2
O2
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3. Complete Oxidation (Burning or Combustion)
Burning of C, H, O - containing molecules in the
presence of oxygen CxHyOz O2 CO2
H2O C3H8 O2 3 CO2 4
H2O Propane oxygen carbon
dioxide water
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The complete oxidation of hydrocarbons by burning
in the presence of oxygen gas always yields CO2
and H2O as products!
The combustion of glucose C6H12O6 6O2
? 6CO2 6H2O
Methane gas burns to produce carbon dioxide gas
and gaseous water whenever something burns it
combines with O2(g) CH4(g) O2(g) ? CO2(g)
H2O(g)
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Combustion Products

• To predict the products of a combustion reaction,
  combine each element in the other reactant with
  oxygen

If the Reactant The Combustion Product is
contains C CO2(g)
contains H H2O(g)
contains S SO2(g)
contains N NO(g) or NO2(g)
contains metal M2On(s)
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4. Double-Replacement Prec. Rxns
Ions exchange with oppositely-charged ions to
form a precipitate AX BY
AY BX NaCl AgNO3
NaNO3 AgCl(s)
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5. Double-Replacement Neutralization Rxn
The acid and base neutralize each other in a
neutralization reaction and water is formed. An
ionic compound called a salt is also formed
HX MOH H2O MX acid
base water salt
HCl NaOH H2O NaCl
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Double Displacement Reactions

• Two ionic compounds exchange ions during a
  reaction.
• It may be followed by decomposition of one of the
  products to produce a gas.
• X ÅYq (aq) A ÅBq (aq) XB AY
• Precipitation, acid-base and gas-evolving
  reactions are all examples of double displacement
  reactions.

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6. Redox Rxns
Single-replacement reduction-oxidation reactions
(redox) - reaction looks as if one element is
replacing another A BX
AX B Cu AgNO3 CuNO3
Ag
What is reduction? What is oxidation? It is the
gaining or losing of electrons - more later
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Displacement of Copper by Zinc
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Classifying Reaction Type
Equation Type A X AX AX
A X CxHyOz O2
CO2 H2O A BX AX
B AX BY AY
BX HX MOH H2O MX
Reaction Type Combination Decomposition Complete
oxidation Single-replacement redox Double
replacement Precipitation Neutralization
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Classifying Reaction Type
Classify the following as one of the six reaction
types
Mg N2 C3H7CHO O2 HgO Zn(OH)2
H2SO4 Combo, oxidation, decomp, 2 repl. neut.