Why??? As you’ve already seen… Chemical reactions occur around us everyday--- so many in fact that looking at them all individually would be REALLY overwhelming! So instead we name them based what happens!

Classification of Chemical Reactions Chemical reactions can be classified in one of two ways: Based on atoms moving (rearrangement) Based on how energy/ heat is transferred Vs.

Classifying based on atoms moving

where A and B may be either elements or compounds. 1) Synthesis Reaction Boy + Girl = Couple This is a reaction in which two or more elements or compounds combine to form a single product. This type of reaction follows the general equation A + B  AB where A and B may be either elements or compounds.  +

Example: Synthesis Burning Magnesium 2Mg + O2  2MgO

Decomposition Reaction The couple breaks up! In this type of reaction a single reactant, a compound, breaks into two or more parts. Often these are the most difficult to predict. Here is the general equation: ABA + B where A and B may be either elements or compounds. + 

Example: Decomposition Hydrogen Peroxide 2H2O2 2H2O +O2

Single Replacement Reaction + +  Single Replacement Reaction In this type of reaction, a more reactive element replaces a less reactive element in a compound. For the metals, you will need to use an activity series (like the one in your notes)– the higher the element is the more REACTIVE it is. The general equation: A + BC  AC + B where A is a metal. A + BC  C + BA Like one girl switching dance partners!

Example: Single Replacement Magnesium and Carbon Dioxide 2Mg + CO2  2MgO + C

Double Replacement Reaction + +  Double Replacement Reaction In this type of reaction, two compounds react to form two new compounds. The formation of a molecular compound such as water, the formation of a gas, or the formation of a precipitate usually drives these reactions. Here’s the general equation: AB + CD  AD + CB Note: “Metals” replace “metals” and non-metals replace non-metals Like 2 pairs of dancers changing partners

Example: Double Replacement Potassium Iodide and Lead (II) Nitrate 2KI(aq) + Pb(NO3)2(aq)  2KNO3(aq) + PbI2(s) 

CxHy + O2(g)  CO2(g) + H2O(l) or (g) Combustion Reaction In this type of reaction, a hydrocarbon is burned in the presence of oxygen gas to form carbon dioxide and water. Here is the general equation in the presence of plenty of oxygen: CxHy + O2(g)  CO2(g) + H2O(l) or (g) Note: If combustion is inefficient (insufficient oxygen) then carbon monoxide is formed!

Example: Combustion Burning Methane (Natural Gas) CH4 + 2O2  CO2 + 2H2O 

Neutralization Reactions Unfortunately we cannot forget about neutralization reactions (a.k.a. acid-base reactions)!  In this type of reaction, an acid and a base react to form a salt and water. The general equation for this type of reaction is: HX + MOH  MX +H2O Where M is a metal ion and X is a non-metal ion

Classifying based on energy transfer

Endothermic vs. Exothermic Reactions are classified by looking at whether energy is required or released during a chemical reaction: EXOTHERMIC (exo= outside)- energy is released during a chemical reaction (i.e. is a product), given off as heat ENDOTHERMIC (endo= inside)- energy is required during a chemical reaction (i.e. is a reactant), and heat is absorbed

Example of an Exothermic Reaction: Decomposition of H2O2

Example of an Endothermic Reaction: The “Green” Cold pack— Ammonium Nitrate in Water

Six Questions to find the type of Chemical Reaction Follow this series of questions. When you can answer "yes" to a question, then stop! 1) Does your reaction have oxygen as one of it's reactants and carbon dioxide and water as products? If yes, then it's a combustion reaction 2) Does your reaction have two (or more) chemicals combining to form one chemical? If yes, then it's a synthesis reaction 3) Does your reaction have one large molecule falling apart to make several small ones? If yes, then it's a decomposition reaction

Six Questions to find the type of Chemical Reaction cont. 4) Does your reaction have any molecules that contain only one element? If yes, then it's a single displacement reaction 5) Does your reaction have water as one of the products? If yes, then it's an acid-base reaction 6) If you haven't answered "yes" to any of the questions above, then you've got a double displacement reaction

Practice Problems Fe2O3  C18H38 +O2  Al + NiBr2  Li + N2  Cl2 + NiBr2  AgNO3 + Na2CrO4  HCl + Mg(OH)2 

Fe2O3  Skeleton Equation: Fe2O3  Fe + O Balanced Equation:

Al + NiBr2  Skeleton Equation: Al + NiBr2  Ni + AlBr3 Balanced Equation: 2Al + 3NiBr2  3Ni + 2AlBr3

Cl2 + NiBr2  Skeleton Equation: Cl2 + NiBr2  Br2 + NiCl2 Balanced Equation:

HCl + Mg(OH)2  Skeleton Equation: HCl + Mg(OH)2  MgCl2 + H2O Balanced Equation: 2HCl + Mg(OH)2  MgCl2 + 2H2O

C18H38 +O2  Skeleton Equation: C18H38 +O2  CO2 + H2O Balanced Equation: 2C18H38 + 55O2  36CO2 + 38H2O

Li + N2  Skeleton Equation: Li + N2  Li3N Balanced Equation:

AgNO3 + Na2CrO4  Skeleton Equation: AgNO3 + Na2CrO4  NaNO3 + Ag2CrO4 Balanced Equation: 2AgNO3 + Na2CrO4  2NaNO3 + Ag2CrO4