Types of Chemical Reactions

1. Synthesis Reactions A synthesis reaction occurs when two or more simple substances combine to produce a more complex substance. AKA: Combination reaction. The general equation for a synthesis is: A + B  AB HINT: If there is only one product – it is likely a synthesis. Examples of Synthesis Reactions CO2 + H2O  H2CO3 4Fe + 3O2  2Fe2O3 Li2O + H2O  2LiOH

2. Decomposition Reactions A decomposition reaction occurs when a complex substance is broken down into two or more simpler substances. Heat is often used to aid in decomposition reactions – these reactions that employ heat are called thermal decompositions. Decompositions and synthesis reactions are opposites. The general equation for a decomposition reaction is: AB  A + B HINT: If there is only one reactant – it is likely a decomposition reaction. Examples of Decomposition Reactions: NH4NO3  N2O + 2H2O Ca(OH)2  CaO + H2O 2H2O2  2H2O + O2

3. Single Displacements A single displacement reaction occurs when a single element takes the place of one of the elements in a compound. AKA: Single Replacement The general equation for a single displacement reaction is: AB + Z  ZB + A Metals displace metals while nonmetals displace nonmetals. HINT: The single mysterious loner moves into town and breaks up the happy couple! Examples of Single Displacement Reactions Fe + CuSO4  FeSO4 + Cu 2K + MgO  K2O + Mg 2CuF + Ba  BaF2 + 2Cu

Li K Ba Ca Na Mg Al Zn Fe Ni Sn Pb H Cu Hg Ag Au Not So Fast There… The lone element doesn’t always break up the couple! We can use a tool called the activity series to predict if the compound will stay together or break up. The activity series is a list of metals and hydrogen that are arranged in order of reactivity. Li K Ba Ca Na Mg Al Zn Fe Ni Sn Pb H Cu Hg Ag Au The rule is that you can only be displaced by an element that is to the left of you. This makes Lithium the strongest and Gold the weakest. There is also a halogen activity series – it is used to predict reactions with halides. F Cl Br I

4. Double Displacements A double displacement reaction always involves two ionic compounds that switch partners with each other. Again, positive ions switch with positive ions (and/or vice-versa). The general equation for a double displacement reaction is: AB + XY  AY + XB HINT: Two couples switch partners at the dance. Examples of Double Displacement Reactions: Pb(NO3)2 + 2KI  PbI2 + 2KNO3 Na2SO3 + 2HCl  2NaCl + H2SO3 2NaOH + H2SO4  2H2O + Na2SO4

5. Combustion Reaction A combustion reaction occurs when a substance (the “fuel”) reacts very rapidly with oxygen to form carbon dioxide and water. Combustion reactions release a good deal of energy in a very short period of time. The general equation for a combustion reaction is: Fuel + O2  CO2 + H2O HINT: Something combines with oxygen to produce carbon dioxide and water.