Types of Chemical Reactions

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Chapter 8

• Types of Chemical Reactions

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Will the reaction occur?

• If you light a candle, it burns and makes carbon
  dioxide and water. Why doesnt the reverse
  reaction occur? Why cant you make a candle from
  carbon dioxide and water?

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Will the reaction occur?

• Driving forces
• Forming a solid (precipitate)
• Transfer of electrons
• Forming water
• Forming a gas
• Yes, a reaction will occur if one of these things
  can happen.

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Dissolving ions

• A strong electrolyte completely separates into
  ions when it is mixed with water.
• Example NaCl
• Complete the equation of silver nitrate
  dissolving in water
• AgNO3(s) ?

NaCl(S)
Na(aq) Cl-(aq)
H2O
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Precipitates

• If you mix NaCl(aq) and AgNO3 (aq) , what
  possible products could form?
• NaCl(aq) and AgNO3 (aq) ? ?
• The anions (Cl- and NO3-)change places.
• NaCl(aq) and AgNO3 (aq) ? NaNO3(aq) AgCl(s)
• AgCl is a precipitate, so write an (s)
• A precipitate is an insoluble solid. Insoluble
  it cannot dissolve in water.
• What is the driving force in this reaction?

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Double replacement (continued)

• A double replacement reaction happens when a
  precipitate forms.
• Reactants must be aqueous (dissolved in water)
• Example NaCl dissolved would be shown as
  NaCl(aq)
• Solubility chart on page 245 will show you when a
  precipitate will form.
• Example KNO3
• Soluble or insoluble?
• Rule 2 K salts are usually soluble.
• Answer Soluble (No precipitate)

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Will this double replacement actually happen??

• Practice Will this form a reaction?
• Write the formulas of the possible products
  (Inside and outside)
• Use the solubility chart to determine if any of
  the products are INSOLUBLE.
• If one or both products are insoluble, a chemical
  reaction will happen.

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• Examples
• KNO3 and BaCl2
• KOH and Fe(NO3)3
• Na2SO4 and Pb(NO3)
• Annimation http//www.mhhe.com/physsci/chemistry/
  animations/chang_7e_esp/crm3s2_3.swf

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Double Replacement

• You should be able to write three types of
  chemical equations for double replacement
• 1. Molecular equation
• 2. Complete ionic equation
• 3. Net ionic equation

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Double Replacement

• The molecular equation shows the complete
  formulas of all reactants and products
• NaCl(aq) AgNO3 (aq) ? NaNO3(aq) AgCl(s)
• The complete ionic equation shows all strong
  electrolytes (aq) as ions.
• Na(aq) Cl-(aq) Ag(aq) NO3-(aq)?Na(aq)
  NO3-(aq AgCl(s)

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Double Replacement

• The net ionic equation shows only the chemicals
  participating in the reaction.
• Steps
• Remove the spectator ions
• Spectator ions are the same on the reactant side
  and the product side (Na and NO3-)
• Na(aq) Cl-(aq) Ag(aq) NO3-(aq)?Na(aq)
  NO3-(aq AgCl(s)
• Net ionic equation
• Cl-(aq) Ag(aq) ? AgCl(s)

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8.2

• Acid-Base Reactions and
• Oxidation-Reduction Reactions

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Arrhenius Acids and Bases

• An Arrhenius Acid is a substance that produces H
  ions when dissolved in water.
• A strong acid is an acid that is a strong
  electrolyte. It completely separates into H and
  the anion.
• HCl ? H Cl-
• Strong acids HCl, HNO3 and H2SO4

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Arrhenius Acids and Bases

• An Arrhenius Base produces OH ions when dissolved
  in water.
• A strong base completely separates into a metal
  cation and OH-
• NaOH ? Na OH-

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Acid-Base Reaction

• Write the molecular equation, complete ionic
  equation and net ionic equation for the reaction
  of hydrochloric acid and sodium hydroxide.
• Molecular equation
• HCl NaOH ? H2O NaCl
• Complete ionic equation
• H Cl- Na OH- ? H2O(l) Na Cl-
• Net ionic equation
• H OH- ? H2O(l)

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Acid-Base Reaction

• When an acid and base are mixed, the products are
  always water and a salt.
• How do you know a reaction happened? The
  solution will be hot.
• An acid-base reaction is the reaction of H and
  OH-

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Oxidation Reduction

• In an oxidation-reduction reaction, electrons
  move from one chemical to another.
• Common reactions
• A metal and a nonmetal react
• Reactions between nonmetals where O2 is a
  reactant or product.

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Oxidation Reduction
2 electrons

• Ca(s) Cl2(g) ? CaCl2(s)
• Which chemical is losing electrons? How many
  electrons?
• Ca loses two electrons
• Which chemical is gaining electrons? How many
  electrons?
• Cl gains one electron

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Oxidation Reduction

• This happens in two stepsCa? Ca2 2e-
• Cl e- ? Cl-
• Draw a picture of this reaction
• Mg(s) CuCl2(s) ? Cu(s) MgCl2(s)
• Which chemical loses electrons? How many?
• Which chemical gains electrons? How many?

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8.3Types of reactions How do we know IF it
will happen?
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Classifying reactions

• Looking at a chemical equation, be able to
  classify it
• Based on driving force
• 1. Precipitation reactions
• 2. Oxidation-reduction reactions
• 3. Acid-base reactions
• Types of oxidation-reduction reactions
• 1. Combustion reactions
• 2. Synthesis reactions
• 3. Decomposition reactions
• 4. Single Replacement

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Double Replacement

• AXBY ? AY BX
• Each anion changes places with the cation.
• Example sodium sulfate copper (II) chloride

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• Single Replacement
• ABX ? AX B
• A a metal or group 7 element.
• B metal, group 7 element or hydrogen
• X anion
• A replaces B in the BX compound.
• Example
• Zn(s) 2HCl(aq) ? H2(g) ZnCl2(aq)

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Synthesis Reactions

• Synthesis 2 or more substances combine to form
  one, bigger molecule.
• General formula
• Example Combustion of Ca
• Ca O2 ? CaO

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Decomposition Reactions

• Decomposition one substance splits to form
  several smaller molecules/atoms.
• General formula
• Example Breaking water molecules.
• What equation will it have? (its a reaction that
  results in Hydrogen gas, H2, and Oxygen,O2)
• Usually requires energy input (heat, electricity,
  etc), because we are breaking bonds.

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Combustion Reactions
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Combustion Reactions

• Combustion a substance combines with oxygen.
  When they react they release energy, water vapor
  and carbon dioxide.
• Will need to balance these
• Ex C2H5OH O2 ? CO2 H2O

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Classifying reactions

• Practice Classify this reaction in as many ways
  as possible
• 2Ca O2 ? 2CaO
• This is classified as a synthesis and combustion.
  It is also an oxidation-reduction reaction.