Chapter 8 Chemical Reactions

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Chapter 8 Chemical Reactions

• Chemistry by Addison - Wesley

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8.1 Describing Chemical Change

• Word Equations
• In a chemical reaction, one or more substances
  change into one or more new substances
• Reactants Products
• Important to note that in a chemical reaction the
  atoms are neither created or destroyed just
  rearranged

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Chemical Equations

• Chemical equation is similar to a word equation
  only chemical symbols represent substances
• Skeleton equation represents the compounds
  without a quantity
• State of matter can also be added to a skeleton
  equation
• H2 (g) O2 (g) H2O (l)

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Balancing Equations

• Rules for Balancing Equations
• Determine the correct formulas for the reaction
• Write the formula with the reactants on the left
  and the products on the right
• Count the number of atoms of each element on each
  side
• Balance the elements one at a time using
  coefficients
• Check each atom to make sure that it is balanced
• Make sure the coefficients are in the lowest
  possible ratio

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Examples

• Turn to page 209

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8.2 Types of Chemical Reactions

• Classifying reactions
• Five Categories
• Combination
• Decomposition
• Single-replacement
• Double-replacement
• Combustion

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Combination Reactions

• In a combination reaction, two or more substances
  combine to form a single substance
• Two or more reactants
• One product
• H2 O2 -gt H2O

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Examples

• Turn to page 214

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Decomposition Reactions

• In a decomposition reaction, one substance breaks
  down into two or more substances
• One Reactant
• Two or more products
• H2O -gt H2 O2
• Often require heat or some sort of energy source
  to break down bonds in the compound

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Examples

• Turn to page 216

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Single-Replacement Reactions

• In a single-replacement reaction, one element
  replace another in a compound
• Two reactants
• Two products
• Na HCl -gt H2 NaCl
• Normally, the replacement occurs at the cation
  spot

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Examples

• Turn to page 218

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Double-Replacement Reactions

• In a double-replacement reactions, two compounds
  exchange cations
• Two reactants
• Two products
• NaOH HCl -gt H(OH) NaCl
• In most cases, one of the following will occur in
  a double-replacement reaction 1) a precipitate
  forms, 2) a gas forms, or 3) a molecular compound
  forms

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Examples

• Turn to page 220

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Combustion Reactions

• In combustion reactions, a compound reacts with
  oxygen often to produce heat or light
• One of the reactants will always be oxygen
• A hydrocarbon is often the other reactant
• Combustion of a hydrocarbon will produce H2O and
  CO2
• C2H6 O2 -gt H2O CO2 heat

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Examples

• Turn to page 221

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8.3 Reactions in Aqueous Solutions

• Net Ionic Equation
• In an aqueous solution, compounds ionize into
  solution
• Ions that are on both sides of the equation are
  called spectator ions
• These ions cancel out of the equation
• Net Ionic Equation

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Predicting the Formation of a Precipitate

• Solubility Rules for Ionic Compounds
• Salts of alkali metals and ammonia - soluble
  (exceptions some lithium compounds)
• Nitrate salts and chlorate salts - soluble (few
  exceptions)
• Sulfate salts - soluble (Compounds of Pb, Ag, Hg,
  Ba, Sr, and Ca are exceptions)
• Chloride salts - soluble (Ag and some Hg and Pb
  are exceptions)
• Carbonates, phosphates, chromates, sulfides, and
  hydroxides - insoluble (Alkali metals and ammonia)