Classification of Chemical Reactions

Types of Chemical Reactions Synthesis Decomposition Single Replacement Double Replacement Combustion

Synthesis Reactions A reaction in which two or more simple substances (elements or compounds) react to form one new substance. A + B  AB Example: 2H2 + O2  2H2O CaO + CO2  CaCO3

Decomposition Reactions A reaction in which one substance breaks down into two or more simple substances AB  A + B Example: 2H2O2  2H2O + O2 2KClO3  2KCl + 3O2

Single Replacement Reactions A reaction in which an uncombined element replaces another element in a compound A + BC  AC + B “Like replaces like” – metals replace metals and nonmetals replace nonmetals

Single Replacement Reactions (continued) Examples: Mg + CuSO4  MgSO4 + Cu (Mg and Cu are both metals) Cl2 + NaBr  NaCl + Br2 (Cl and Br are both nonmetals) In order for the reaction to take place, the uncombined element must be more reactive than the ion it is replacing.

Reactivity Table Most Active Metals Li Rb K Ca Na Mg Al Mn Zn Fe Ni Sn Pb Cu Ag Least Active Metals Pt Au Most Active Nonmetals F Cl Br I Least Active Nonmetals

Which of the following reactions can take place? I2 + NaF  F2 + NaI Mg + HCl  MgCl2 + H2 Cu + MgSO4  CuSO4 + Mg K + NaOH  KOH + Na

Double Replacement Reactions A reaction in which two positive ions replace each other in compounds AB + CD  AD + CB In order for this type of reaction to occur, one of the following must happen: a precipitate is formed, a gas is formed, or one of the products must be covalent.

Double Replacement Reactions (continued) Examples: Na2S + Cu(NO3)2 CuS+ 2NaNO3 (a precipitate is formed) 2NaCN + H2SO4 2HCN + Na2SO4 (a gas is formed) NaOH + HCl  NaCl + H2O (a covalent compound is formed)

Combustion Reaction A reaction in which a hydrocarbon reacts with oxygen to produce carbon dioxide and water CxHy + O2  CO2 + H2O Example: CH4+ 2O2 CO2 + 2H2O C6H12O6 + 6O2  6CO2 + 6H2O

Review Classify each of the following reactions by type and then balance the equation: Pb(NO3)2 + K2CrO4PbCrO4+ KNO3 Cl2 + KI  KCl + I2 C3H6 + O2  CO2 + H2O Al(OH)3  Al2O3 + H2O Li + O2  Li2O HCl + Fe2O3  FeCl3 + H2O MgCO3  MgO + CO2 Ba(CN)2 + H2SO4  HCN + BaSO4

Classifying Reactions Based on Energy Changes Exothermic reactions are reactions in which heat/energy is released Example: 2C4H10 + 13O2  8CO2 + 10H2O The container often feels warm during exothermic reactions reactions involving explosions and burning are examples

Classifying Reactions Based on Energy Changes (continued) Endothermic reactions are reactions in which heat/energy is absorbed Example: 6CO2 + 6H2O C6H12O6 + 6CO2 (photosynthesis) NaHCO3 + HCl  NaCl + H2O + CO2 The container often feels cold during endothermic reactions Reactions involving cooking or heating are often examples

Review Baking a cake Exploding dynamite Burning a piece of paper Identify each of the following as either exothermic or endothermic: Baking a cake Exploding dynamite Burning a piece of paper A chemical ice pack Hand warmers