Unit 11: Classification of chemical reactions

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Unit 11 Classification of chemical reactions

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Chemical Reactions

• a process that involves changes in the structure
  and energy content of atoms, molecules, or ions
  but not their nuclei.

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Formation of Solutions - Dissolving

• A solute dissolving in a solvent requires energy.
• It can be an endothermic or exothermic process.
• But, is it a chemical reaction?

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Formation of Solutions- Dissolving

• Covalent molecules DO NOT break apart when
  dissolved.
• Ionic Compounds DO break apart when dissolved
  (This is considered a chemical change.)

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Law of Conservation of Matter

• matter cannot be created or destroyed, it can
  only change forms. Therefore, in a chemical
  reaction the number of atoms, the mass and the
  charge must be conserved.

reactants
products
Activated complex
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Equations

• Taking an Inventory and Balancing In order to
  be balanced, be the same on the reactant and
  product side of the equation

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Balancing Equations-Taking inventory

• Reactants
• 4 hydrogen
• 2 oxygen

• Products
• 4 hydrogen
• 2 oxygen

In order to be balanced, the type and number of
atoms must match on the reactant and product side
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Tutorial and Practice

• Tutorial
• Practice

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• __H2S(g) __SO2(g) ? __S(s) __H2O(g)
• Reactants Products

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• __Fe2O3(s) __H2(g) ? __Fe(s) __H2O(g)
• Reactants Products

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Single Replacement

• A single element replaces another element in a
  compound.
• a metal replaces another metal (or hydrogen) OR
• a nonmetal replaces another nonmetal (think back
  to the reactivity trend for nonmetals,
  specifically the halogens.)

• ___Cu (s) __AgNO3 (aq) ? __Cu(NO3 )2 (aq) ___Ag
  (s)
• SR animation

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Using the activity series

• Determine if the element by itself is a metal or
  a nonmetal.
• If it is a metal, circle the metal in the
  compound.
• Then, look on the activity series (on back of EOC
  periodic table)
• If metal by itself is higher (more active) than
  the metal you circled, then it WILL replace the
  other metal and the REACTION WILL TAKE PLACE.
• If metal by itself is lower (less active) than
  the metal you circled, then it WILL NOT replace
  the other metal and NO REACTION WILL OCCUR.
• If it is a nonmetal, circle the nonmetal in the
  compound.
• Then, look on the periodic table. Remember,
  fluorine is the most active nonmetal.
• If nonmetal by itself is more active than the
  nonmetal you circled, then it WILL replace the
  other nonmetal and the REACTION WILL TAKE PLACE.
• If nonmetal by itself is less active than the
  nonmetal you circled, then it WILL NOT replace
  the other nonmetal and NO REACTION WILL OCCUR.

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Practice

• F2 (g) AlCl3 (aq) ? ?
• Ag (s) FeCl2 (aq) ? ?

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Double ReplacementClue Do-See-DohAB CD ?
AD CB
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Double Replacement

• Two reacting compounds, with metals trading
  places.
• A precipitate (insoluble solid) is usually
  formed. Use solubility rules to determine if a
  product is soluble (aq) or an insoluble ppt (s)

___AgNO3 (aq) ____NaCl (s) ? ____NaNO3 (aq)
____AgCl (s)
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Determining solubility of products

• Use the solubility rules on the back of the
  periodic table.
• The solubility rules are organized by the anion
  in the compound.
• Find the anion.
• Determine if, based on the cation, the compound
  is soluble (aq) or insoluble (s) in water.
• Write the (aq) or (s) after the compound
• Practice
• AgCl
• KNO3
• PbS

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More Types of Reactions

• Combustion CxHy O2 ?CO2 H2O
• Redox any reaction where the oxidation number
  of two species changes
• Precipitation a double replacement reaction
  that produces a ppt.

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Combustion

• Definition a process which converts the
  potential energy of fuels (comprised primarily of
  carbon and hydrogen, like propane) into kinetic
  energy (heat and light)
• What burns is the only thing that changes in
  these reactions.
• Example _C3H8 _O2 ? _ CO2 _H2O energy

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OXIDATION-REDUCTION REACTIONS

• a reaction where electrons are transferred
  between reactants and products

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OXIDATION-REDUCTION REACTIONS

• a. Loss of Electrons is OXIDATION
• oxidation number increases from reactant side to
  product side.
• Gain of Electrons is REDUCTION
• oxidation number decreases from reactant side to
  product side.
• These must occur together. Cant have one
  without the other.

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OXIDATION-REDUCTION REACTIONS

• How to identify a redox reaction
• Determine the oxidation number of each element in
  each compound.
• Compare the reactants and products.
• If there is a change in the oxidation number of
  any species, then it is redox.

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Determining oxidation numbers

• The oxidation of an atom is the charge it would
  have if it was in a compound composed of ions.
• Rules
• ox. of neutral atoms AND diatomics is 0. (ex.
  Fe, O2)
• ox. is to charge for simple ions (Cl-1)
• Sum of ox. in a neutral compound is 0.
• H is 1when combined with another nonmetal.
• H is -1 when combined with a metal.

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OXIDATION-REDUCTION REACTIONS

• Practice- are the following redox reactions?
• ______ a. NaCl AgNO3 --gt NaNO3 AgCl
• ______ b. FeCl2 Cl2 ? FeCl3