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II. Five basic types of chemical reactions: B. Decomposition: A single compound breaks down into its component parts or simpler compounds. Basic form: AX A + X Examples of decomposition reactions: Metallic carbonates, when heated, form metallic oxides and CO2 . ex. CaCO3 CaO + CO2 Most metallic hydroxides, when heated, decompose into metallic oxides and water. ex. Ca(OH)2 CaO + H2O Metallic chlorates, when heated, decompose into metallic chlorides and oxygen. ex. 2KClO3 2KCl + 3O2 Some acids, when heated, decompose into nonmetallic oxides and water. ex. H2SO4 H2O + SO3 Some oxides, when heated, decompose. ex. 2HgO 2Hg + O2 Some decomposition reactions are produced by electricity. ex. 2H2O 2H2 + O2 ex. 2NaCl 2Na + Cl2 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 Example Decomposition of ammonium dichromate Practice Predicting Products of Decomposition Reactions 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: 1. a precipitate 2. a gas 3. water or some other non-ionized substance. Basic form: AX + BY AY + BX Examples of ionic reactions: #3: Formation of water. (If the reaction is between an acid and a base it is called a neutralization reaction.) ex. HCl + NaOH NaCl + H2O #2 Formation of a gas. ex. HCl + FeS - FeCl2 + H2S H2S is the only gas you need to remember. Look for one of these three. Rewrite equation, replacing unstable compound with products. Ex. NH4Cl + Ca(OH)2 NH4OH + CaCl2 NH4Cl + Ca(OH)2 NH3 +H2O + CaCl2 Now balance the equation! Note the up arrow. You must indicate that a gas is produced! #1 Formation of precipitate. (A solid that was not present in the reactants) Marked with (s) or Use Solubility Table S mean soluble, or dissolved. No precipitate is formed. ALL OTHER LETTERS MEAN THAT A PRECIPITATE FORMS. Look up the formulas for your products. Whichever forms a precipitate is marked with (s) or . Any soluble products are marked (aq). If no solid forms, write N.R. for no reaction. Magnesium acetate + sodium carbonate Think: It's not an acid + base. What are the products? magnesium carbonate and sodium acetate Any unstable product? Look for H2CO3, H2SO3, NH4OH Not there. Now check for a precipitate. Magnesium carbonate has a P solid forms. Finish equation with a down arrow or (s) after the magnesium carbonate. Example Ammonium chloride + barium hydroxide Practice Predicting Products of Ionic Reactions Combustion of Hydrocarbons: Hydrocarbons contain hydrogen and carbon. Some also have oxygen. When a hydrocarbon is burned with sufficient oxygen supply, the products are always carbon dioxide and water vapor. Balance in this order: C, H, O 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. NOTE: The phrase "To burn" means to add oxygen unless told otherwise. (CxHy) + O2 CO2 + H2O ex. CH4 + 2O2 CO2 + 2H2O ex. 2C4H10 13O2 8CO2 + 10H2O 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 Examples of replacement reactions: ex. Fe + CuSO4 FeSO4 + Cu 2. Replacement of hydrogen in water by an active metal. ex. 2Na + 2H2O 2NaOH + H2 Only one hydrogen is replaced, leaving an hydroxide ion. Only these metals will react with water, producing hydrogen gas and metallic hydroxide. 3. Replacement of hydrogen in acids by active metals. ex. Zn + 2HCl ZnCl2 + H2 Only these metals will react with acids, producing hydrogen gas and metallic hydroxide. ex. Cl2 + 2NaBr 2NaCl + Br2 The halogen is replaced, NOT the metal! The halogen activity series is Group 17 on the Periodic Table. Examples A. Synthesis (composition): two or more elements or compounds may combine to form a more complex compound. Basic form: A + X AX Examples of synthesis reactions Metal + oxygen metal oxide ex. 2Mg + O2 2MgO Nonmetal + oxygen nonmetallic oxide ex. C + O2 CO2 Metal oxide + water metallic hydroxide ex. MgO + H2O Mg(OH)2 Nonmetallic oxide + water acid ex. CO2 + H2O H2CO3 Metal + nonmetal salt ex. 2 Na + Cl2 2NaCl A few nonmetals combine with each other. ex. 2P + 3Cl2 2PCl3 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 Example Zinc + Iodine zinc iodide Click on pictures Oxygen + Hydrogen Water Practice Predicting Products of Synthesis Reactions Analyzing Chemical Reactions One Reactant? no yes Decomposition One Product? yes Synthesis no Next slide 2 Ionic Compounds or Acid and Ionic Compound? yes no Double Replacement Precipitate Neutralization Gas Next slide Element and Compound? yes Single Replacement Metal no Hydrocarbon and O2 Halogen Metallic oxide no no yes Combustion ???? yes One Reactant? no One Product? Decomposition yes no Synthesis 2 Ionic Compounds or Acid and Ionic Compound? yes no Double Replacement Element and Compound? yes Precipitate Gas no Neutralization Hydrocarbon and O2? Single Replacement no ???? no yes Combustion