Summary of Reaction Types：反应类型综述.doc

NOTES #5: Summary of Reaction TypesCOMBINATION (or synthesis) REACTIONSIn combination reactions, two or more simple substances are combined to form one or more new complex substances. The general form for combination reactions is:element (or compound) + element (or compound) compound(s) A + B C A + B + C D1. Two or more elements combine to form a single compound.2. An acid anhydride (nonmetallic oxide) combines with water to form an acid.3. A basic anhydride (metallic oxide) combines with water to form a base.4. A basic anhydride combines with an acid anhydride to form a salt.DECOMPOSITION REACTIONSWhen energy in the form of heat, electricity, light, or mechanical shock is supplied, a compound may decompose to form two or more simpler substances. The general form for this type of chemical reactions is: compound two or more substances AB A + B ABC AB + C (or A + B + C ) 1. When some acids are heated, they decompose to form water and an acidic oxide (nonmetallic oxide).2. When some metallic hydroxides are heated, they decompose to form a metallic oxide and water.3. When some metallic carbonate are heated, they decompose to form a metallic oxide and carbon dioxide.4. When metallic chlorates are heated, they decompose to form metallic chlorides and oxygen.5. Most metallic oxides are stable and do not readily decompose when heated. A FEW do decompose when heated.6. Some compounds cannot be decomposed by heating, but can be decomposed by electricity into their elements. SINGLE DISPLACEMENT REACTIONSIn single displacement reactions, one element displaces another element in a compound. A single displacement reaction has the general form: element + compound element + compound A + BX B + AX or X + CM M + CX 1. An active metal will displace a less active metal in a compound.2. Active metals (Group 1, the alkali metals; Group 2, the alkaline earth metals) will react with water to form a metallic hydroxide and hydrogen gas. (The hydrogen is displaced.)3. Active metals such as Na, K, Mg, Ca, Zn, Fe, and Al will displace the hydrogen in acids to form a salt and hydrogen gas.4. An active nonmetal will displace a less active nonmetal in a compound.DOUBLE DISPLACEMENT REACTIONSIn double displacement reactions, the positive and negative ions of two compounds are exchanged. The general form for double displacement reactions is: compound + compound compound + compound AX + CY AY + CX1. A reaction between an acid and a base yields a salt and water. Such a reaction is called a neutralization reaction. Usually the salt is soluble in water and it is difficult to tell if a reaction has occurred. If the water is evaporated, the salt will be left behind as a solid.2. Reaction of a salt with an acid forms a salt of the acid and a second acid that is volatile (forms a gas). Some acids and bases react with salts to form a compound that can be composed. For example, carbonic acid (H2CO3(aq), sulfurous acid(H2SO3(aq), and ammonia (NH3(aq) decompose to give a gas and water:3. Reactions of some soluble salts produce an insoluble salt and a soluble salt.COMBUSTION REACTIONSA combustion reaction is a reaction of a substance with oxygen, usually with the rapid release of heat to produce a flame. Most combustion reactions involve a hydrocarbon compound (contains carbon and hydrogen) that reacts with oxygen to produce carbon dioxide and water (CO2 and H2O). Complete combustion reactions give off energy as heat and a blue flame (nonluminous). Incomplete combustion reactions produce carbon monoxide (CO), water, and unreacted carbon (as soot); these reactions release energy as heat and a yellow flame (luminous). CxHy CO2 + H2OCORROSION REACTIONSA corrosion reaction involves the reaction of oxygen with a metal. Corrosion occurs ONLY when there is water present either in a solution (as in a lake, river, or ocean) containing dissolved oxygen or as a vapor in the atmosphere (humidity). Corrosion does NOT occur in DRY air. Also, pure metals seem to resist corrosion (these metals tend to form a thin coating of the metallic oxide on their surfaces; this oxide is very resistant to further chemical reaction.)