Chemical Equations

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Chemical Equations
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Writing Chemical Equations

• All reactants and products must be correctly
  represented by their proper formulas
• A B ? C D
• Reactants Products
• Law of Conservation of Mass appliesmatter
  neither created or destroyed in chemical
  reactionsboth sides of reaction must have the
  same amount of the same type elements

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Balancing Chemical Equations

• 1. Start with the most complex species present
• 2. Do not change ANY formulas, balance by
  multiplying by the whole formula
• 3. Normally, leave oxygen to the last, exceptions
  happenODD SIDE EVEN rule
• 4. Treat polyatomics as single units if they
  remain unchanged
• 5. Recheck each element to be sure of balance

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Balancing Chemical Equations
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Balancing Chemical Equations
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Oxidation and Reduction

• One important type of reaction is the
  oxidation-reduction reaction. In this type of
  reaction, both oxidation, the losing of
  electrons, and reduction, the gaining of
  electrons, take place. Each reactant not only has
  an operation on itself, but causes the opposite
  reaction the substance reduced is causing
  oxidation of the other, and is thus an oxidizing
  agent the substance oxidized is causing
  reduction of the other, and is thus an reducing
  agent

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Oxidation/Reduction

• An alternate definition for each involves what
  happens to oxygen in the reaction
• oxidationgain of oxygen
• reductionloss of oxygen
• This means that an oxidizing agent will have
  oxygen which it gives away, and the reducing
  agent will receive that oxygen.

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Homework 6a

• p135 CYU all
• p148ff 1, 2, 3, 4, 5

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Mass Relationships in Reactions

• The Mole
• All reactions occur at the molecular level, with
  individual atoms, ions, or molecules doing the
  reacting. Since it is impossible to count out
  these individual units, we need a unit represent
  visible quantities of these.
• The MOLE is defined as the number of atoms in
  exactly 12.0000 grams of C-12
• Mole value 6.02 x 1023 particles of anything
• Counting number like dozen of gross
• Called Avogadros number
• Mole of any atom atomic weight in grams of that
  atom
• Mole of any substance sum of weights of all of
  the atoms in its formula

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Examples
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Formula Weight and the Mole

• Sum of the atomic weights rounded to the nearest
  0.1 unit
• Distribute into parentheses correctly
• One mole of a substance sum of weights
  of all of the atoms in its formula

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Examples
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Converting Between Moles and Other Units

• Particles and moles involve Avogadros number
• Particles ? moles divide by A.N.
• Moles ? Particles. Multiply by A.N.
• Grams and moles involve Molar Mass (MMFormula
  weight expressed in grams)
• g ? moles divide by MM
• moles ? g multiply by MM
• Liters of gas and moles involves Molar Volume
• Molar Volume of any gas at STP 22.4 L/mol
• Liters ? moles divide by 22.4
• Moles ? liters multiply by 22.4
• (Both of these can only be done at STP)

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Mole T

• PARTICLES??MOLES??MASS (grams)
• LITERS of GAS

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Examples
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Homework 6b

• p. 138 CYU
• p. 140 CYU
• p. 141 CYU
• p 149ff 7, 8, 9, 10, 12

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Stoichiometry

• Calculations within reactions-- Bridge Method
• 1. Find reactants and products and write a
  balanced reaction
• 2. Place amount of given substance at top left
  of bridge
• 3. Convert the given to moles if necessary in
  the next span of the bridge
• 4. Change from moles of given substance to
  moles of desired substance in the nest span,
  using coefficients from the balanced equation
• 5. Change from moles to the desired unit in the
  final span of the bridge

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Examples
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Examples
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Examples
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Examples
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Examples
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Homework 6c

• p. 143 CYU
• p. 148 CYU

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Homework 6d

• Turn in as a Lab Group
• p. 150 ff 15, 16, 19, 20, 22, 24

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Homework 6e

• p. 153ff 26, 28, 30, 32
• p. 155 11,12