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II. Five basic types of chemical reactions:
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A. Synthesis (composition):
two or more elements or compounds may combine to form a more complex compound. Basic form: A + X AX
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Examples of synthesis reactions
Metal + oxygen metal oxide ex Mg + O2 2MgO
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Nonmetal + oxygen nonmetallic oxide
ex C + O2 CO2
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Metal oxide + water metallic hydroxide
ex MgO + H2O Mg(OH)2
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Nonmetallic oxide + water acid
ex CO2 + H2O H2CO3
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Metal + nonmetal salt ex Na + Cl2 2NaCl
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A few nonmetals combine with each other.
ex P + 3Cl2 2PCl3
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What do all of these have in common?
2Mg + O2 2MgO C + O2 CO2 CO2 + H2O H2CO3 MgO + H2O Mg(OH)2 2 Na + Cl2 2NaCl 2P + 3Cl2 2PCl3
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Example Zinc + Iodine zinc iodide Oxygen + Hydrogen Water
Click on pictures Oxygen + Hydrogen Water
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Practice Predicting Products of Synthesis Reactions
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B. Decomposition: A single compound breaks down into its component parts or simpler compounds. Basic form: AX A + X
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Examples of decomposition reactions:
Metallic carbonates, when heated, form metallic oxides and CO2 . ex CaCO3 CaO + CO2
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Most metallic hydroxides, when heated, decompose into metallic oxides and water.
ex Ca(OH)2 CaO + H2O
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Metallic chlorates, when heated, decompose into metallic chlorides and oxygen.
ex KClO3 2KCl + 3O2
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Some acids, when heated, decompose into nonmetallic oxides and water.
ex H2SO4 H2O + SO3
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Some oxides, when heated, decompose.
ex HgO 2Hg + O2
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Some decomposition reactions are produced by electricity.
ex H2O 2H2 + O2 ex NaCl 2Na + Cl2
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What do all of these have in common?
CaCO3 CaO + CO2 Ca(OH)2 CaO + H2O 2KClO3 2KCl + 3O2 H2SO4 H2O + SO3 2HgO 2Hg + O2 2H2O 2H2 + O2
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Example Decomposition of ammonium dichromate
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Practice Predicting Products of Decomposition Reactions
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C. Single Replacement: a more active element takes the place of another element in a compound and sets the less active one free. Basic form: A + BX AX + B or AX + Y AY + X
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Examples of replacement reactions:
Replacement of a metal in a compound by a more active metal. ex. Fe + CuSO4 FeSO4 + Cu
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Replacement of hydrogen in water by an active metal.
ex. 2Na + 2H2O 2NaOH + H2 ex. Mg + H2O MgO + H2
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Replacement of hydrogen in acids by active metals.
ex. Zn + 2HCl ZnCl2 + H2
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Replacement of nonmetals by more active nonmetals.
ex. Cl2 + 2NaBr 2NaCl + Br2
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Examples
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D. Ionic or Double Replacement:
occurs between ions in aqueous solution. A reaction will occur when a pair of ions come together to produce at least one of the following: a precipitate a gas water or some other non-ionized substance. Basic form: AX + BY AY + BX
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Examples of ionic reactions:
Formation of precipitate. ex. NaCl + AgNO3 NaNO3 + AgCl ex. BaCl2 + Na2 SO4 2NaCl + BaSO4
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Formation of a gas. ex. HCl + FeS - FeCl2 + H2S
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Formation of water. (If the reaction is between an acid and a base it is called a neutralization reaction.) ex. HCl + NaOH NaCl + H2O
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Formation of a product which decomposes.
ex. CaCO3 + HCl CaCl2 + CO2 + H2O
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Ammonium chloride + barium hydroxide
Example Ammonium chloride + barium hydroxide
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Practice Predicting Products of Ionic Reactions
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Combustion of Hydrocarbons:
When a hydrocarbon is burned with sufficient oxygen supply, the products are always carbon dioxide and water vapor. If the hydrocarbon has an even number of carbons, start with a coefficient of 2 CxHy Balance in this order: C, H, O
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If the supply of oxygen is low or restricted, then carbon monoxide will be produced.
This is why it is so dangerous to have an automobile engine running inside a closed garage or to use a charcoal grill indoors.
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NOTE: The phrase "To burn" means to add oxygen unless told otherwise.
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(CxHy) + O2 CO2 + H2O ex. CH4 + 2O2 CO2 + 2H2O
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Analyzing Chemical Reactions
One Reactant? no yes One Product? Decomposition no yes Next slide Synthesis
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2 Ionic Compounds or Acid and Ionic Compound?
yes no Double Replacement Next slide Precipitate Neutralization Gas
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yes no Element and Compound? Single Replacement Hydrocarbon and O2 no
Metal Halogen Metallic oxide no Combustion ????
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Precipitate Gas Neutralization
One Reactant? yes no One Product? Decomposition yes no Synthesis 2 Ionic Compounds or Acid and Ionic Compound? yes no Double Replacement Element and Compound? yes no Precipitate Gas Neutralization Hydrocarbon and O2? Single Replacement yes no no Combustion ????
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