Double Displacement (or Replacement) Reactions Also referred to as metathesis reaction The two compounds exchange ions to produce two new compounds. It is easier to simply remember that the cations (+ ions) exchange anions (- ions). AB + CD  CB + AD NOTE: always write the cation first then the anion. Many reactions including precipitation and neutralization use the double displacement mechanism.

Double Displacement (or Replacement) Reactions PREDICT THE PRODUCT & BALANCE 1. MgSO4 + LiOH  ___________ 2. Pb(NO3)2 + Na2CO3  ____________ 3. HNO3 + Ba(OH)2  ___________ Answers are on the next slide.

Double Displacement (or Replacement) Reactions ANSWERS 1. MgSO4 + 2 LiOH  Mg(OH)2 + Li2SO4 2. Pb(NO3)2 + Na2CO3  PbCO3 + 2 NaNO3 3. 2 HNO3 + Ba(OH)2  Ba(NO3)2 + 2 H2O Exchange cations

PRECIPITATION REACTION A reaction where an insoluble solid is formed during a reaction between two aqueous solutions. (aq) + (aq)  (aq) + (s) 2KI(aq) + Pb(NO3)2(aq)  2KNO3(aq) + PbI2(s) NEUTRALIZATION REACTION A reaction between an acid and a base which results in the production of a salt and water. HA + BOH  (metal/nonmetal) + H2O HNO3(aq) + KOH(aq)  KNO3(aq) + H2O(l) Exchange cations

Single Displacement (or Replacement) Reactions One element reacts with a compound to produce a different element and a new compound. A + BC  AC + B NOTE: if the element is a metal, it will replace the cation. A + BC  C + BA NOTE: if the element is a nonmetal, it will replace the anion. Many reduction-oxidation reactions use the single displacement mechanism.

Single Displacement (or Replacement) Reactions PREDICT THE PRODUCT 1. Ca + HCl  2. ZnBr2 + I2  3. Cu + AgNO3  Answers are on the next slide.

Single Displacement (or Replacement) Reactions ANSWERS: 1. Ca + 2 HCl  CaCl2 + H2 2. ZnBr2 + I2  ZnI2 + Br2 3. Cu + 2AgNO3  2Ag + Cu(NO3)2

Reduction-Oxidation Reactions A reaction in which electrons are transferred from one species to another. Oxidation means the loss of electrons Reduction means the gain of electrons Rusting is a redox reaction: 4Fe (s) + 3O2 (g)  2Fe2O3 (s) As a reactant Fe has a zero oxidation state but as a product (in Fe2O3) iron has a 3+ oxidation state. Three electrons per atom had to be transferred (lost) in order for this to happen. Note that oxygen also changed from a zero oxidation state to a 2- oxidation state. Oxygen needed to gain 2 electrons per atom.

Reduction-Oxidation Reactions Oxidation means the loss of electrons Reduction means the gain of electrons Electrochemistry involves redox Rx. Cu(s) + 2AgNO3(aq)  2Ag(s) + Cu(NO3)2(aq) The reactant Cu has a zero oxidation state (all elements have a zero oxidation state) but as a product, in Cu(NO3)2,the copper atom loses two electrons and has a 2+ oxidation state. The other atom which acquired the electrons donated by copper is silver. As a reactant silver has a 1+ oxidation state then by gaining electrons from copper, the ions are turned into elemental silver with a zero oxidation state. The net effect of this reaction has metallic copper being oxidized to copper ions and silver ions being reduced to silver metal.

DECOMPOSITION REACTION COMBINATION REACTION A reaction in which two or more substances combine to form a single product. A +B + C  ABC CaO(s) + SO2(g)  CaSO3(s) DECOMPOSITION REACTION A reaction in which a single compound reacts to give two or more substances, usually requiring a raise in temperature. ABC  A + B + C 2KClO3(s)  2KCl(s) + 3O2(g)

COMBUSTION REACTION CH + O2  CO2 + H2O A reaction of a substance with oxygen, usually the rapid release of heat produces a flame. CH + O2  CO2 + H2O 2C4H10(g) + 13O2(g)  8CO2(g) + 10H2O(g) Many times in a combustion reaction, heat energy is given off. In chemical terms this is called an exothermic reaction. Thermochemistry is field of chemistry which studies the transfer of heat in a reaction. The thermodynamic equation representing this exothermic reaction is: 2C4H10(g) + 13O2(g)  8CO2(g) + 10H2O(g) + heat (in Joules)

GAS FORMATION REACTIONS A reaction that produces a gas from reactants not in the gaseous state. 2 HCl (aq) + ZnS (s)  ZnCl2 (aq) + H2S (g) Zn (s) + 2 HCl (aq)  ZnCl2 (aq) + H2 (g) Many gas formation reactions involve two steps, first the double displacement reaction then the decomposition reaction of an unstable substance. Na2CO3 + 2HCl  2 NaCl + H2CO3 H2CO3  CO2 + H2O Besides carbonic acid (H2CO3), sulfurous acid (H2SO3) also decomposes into SO2 and water.

PRACTICE PROBLEMS Write the following as balanced chemical equations then classify each reaction. 1. Magnesium metal is combined with nitrogen at elevated temperatures to form magnesium nitride powder. 2. An aqueous solution of soluble aluminum nitrate is mixed with aqueous sodium hydroxide to produce insoluble aluminum hydroxide and a sodium nitrate solution. 3. Solid potassium sulfite is added to hydrochloric acid to produce sulfur dioxide, water, and potassium chloride. 4. Acetic acid reacts with calcium hydroxide to produce calcium acetate and water. 5. Lithium metal is dropped in water to produce lithium hydroxide and hydrogen gas. 3 Mg (s) + N2 (g)  Mg3N2 (s); combination, redox Al(NO3)3 (aq) + 3NaOH (aq)  Al(OH)3(s) + 3NaNO3(aq) ; ppt, DD K2SO3 (s) + 2HCl (aq)  H2SO3 (aq) + 2KCl (aq) ; DD then H2SO3 (aq)  H2O (l) + SO2 (g) ; decomposition overall Rx : K2SO3 (s) + 2HCl (aq)  H2O (l) + SO2 (g) + 2KCl (aq) 2 HC2H3O2 (aq) + Ca(OH)2 (aq)  Ca(C2H3O2)2 (aq) + 2H2O (l) ; DD, neutralization 2Li (s) + 2H2O(l)  2LiOH (aq) + H2 (g); SD, redox

GROUP STUDY PROBLEMS Write the following as balanced chemical equations then classify each reaction. 1. Solid mercuric oxide decomposes at high temperatures to form metallic mercury and oxygen. 2. Aqueous lead(II) nitrate reacts with aqueous magnesium bromide to produce the insoluble salt lead(II)bromide and soluble magnesium nitrate. 3. At room temperature, aqueous ammonium carbonate is added to hydrochloric acid to produce aqueous ammonium chloride, water and carbon dioxide. 4. Hydrochloric acid is poured over tin metal producing hydrogen gas and tin (IV) chloride. 5. The combustion of ethanol, C2H5OH, results in the production of carbon dioxide and water.