Chemical Reaction Types

Types of reactions Synthesis (Composition) Decomposition Combustion Single-Replacement Double-Replacement Precipitation and Solubility Acid-Base Reduction-Oxidation (Redox)

Synthesis (Composition) Two or more substances combine to form a new compound A + X  AX Examples: Fe + S → FeS H2 + SO3 → H2SO3

Decomposition One compound forms two or more simpler substances AX  A + X Examples: Metallic carbonate → metal oxide + CO2 CaCO3 → CaO + CO2 Metallic hydroxide → metal oxide + H2O Ca(OH)2 → CaO + H2O Metallic chlorate → metal chloride + O2 2 KClO3 → 2 KCl + 3 O2

Combustion A substance combines with oxygen releasing a large amount of energy in the form of heat and light Does not have a true generic form, but hydrocarbons will combust in the presence of oxygen to produce CO2 and H2O Hydrocarbon + O2 → CO­­2 + H2O

Single-Replacement 1 element replaces a similar element in a compound A + BX  AX + B or Y + BX  BY + X Examples: Replacement of a metal with a more active metal Zn + CuSO4 → Cu + ZnSO4 Replacement of hydrogen in water by a metal Ca + 2 H2O → H2 + Ca(OH)2 Replacement of hydrogen in an acid by a metal Zn + H2SO4 → H2 + ZnSO4 Replacement of less active halogen by a more active halogen F > Cl > Br > I Cl2 + 2 KBr → 2 KCl + Br

Double-Replacement The ions of two compounds exchange places in an aqueous solution AX + BY  AY + BX Examples: Formation of a gas FeS + 2 HCl → FeCl2 + H2S ↑ (↑ means gas) Formation of a precipitate (ppt.) NaCl + AgNO3 → NaNO3 + AgCl ↓ (↓ means ppt.) Formation of water NaOH + HCl → NaCl + H2O

Precipitation Reactions A reaction in which two soluble salts react to form an insoluble product is called a precipitation reaction The insoluble product forms a solid and precipitates out of solution The product is called a precipitate

Solubility Rules Most nitrate salts are soluble Most salts of alkali metals and ammonium are soluble

Practice Identify the following as soluble - S or insoluble - I Na2SO4 Pb(NO3)2 PbSO4 NaNO3 KOH Fe(NO3)3 Fe(OH)3 H2SO4 K2Cr2O7 Co(NO3)2 Identify the following as soluble - S or insoluble - I KCl AgNO3 AgCl KNO3 K2CrO4 Ba(NO3)2 BaCrO4 soluble soluble insoluble soluble soluble soluble soluble soluble insoluble insoluble soluble soluble soluble soluble soluble soluble insoluble

Precipitation Reactions Predicting Products Write all reactants as their ions Combine ions that were not combined before Be sure to combine a single type of positive and a single type of negative ion The total charge of the compound must be zero If a product is insoluble, a precipitation reaction has occurred

Examples Predict the products of, write and balance the following reactions. Identify any precipitates. All reactants are aqueous. Potassium hydroxide reacts with barium nitrate Silver nitrate reacts with potassium chloride

Practice Predict the products of, write and balance the following reactions. All reactants are aqueous. 3. Potassium nitrate and barium chloride 4. Sodium sulfate and lead (II) nitrate 5. Potassium hydroxide and iron (III) nitrate

Practice 6a. What compound precipitates when aqueous solutions of Fe2(SO4)3 and LiOH are mixed? 6b. Write a balanced equation for the reaction. 6c. Write the complete ionic equation and the net ionic equation for the above reaction. 6d. Will a precipitate form when solutions of Ba(NO3)2 and KOH are mixed?

Common Acids and Bases (8th) Strong Acids HCl, HI, HBr H2SO4 (1st H) HNO3 Weak Acids HC2H3O2 HF HSO4- NH4+ Strong Bases KOH NaOH Weak Bases NH3

Oxidation-Reduction Reactions A reaction where electrons are transferred from one substance to another Also called redox reactions Used often in biological systems All combustion reactions are redox

Oxidation States To keep track of electrons in redox reactions, we track a numeric concept known as the element’s oxidation state Oxidations states arbitrarily assign electrons to atoms and treat the atoms as if they had the charge imparted by the gain or loss of electrons

Oxidation States The oxidation state of: An atom in its elemental state is zero A monatomic ion is its charge Fluorine is -1 in a compound Oxygen is -2 in a compound (-1 in peroxides) Hydrogen is typically +1 in a compound The elements in a compound or polyatomic ion sum to its charge

Example Assign oxidation states to each atom in: CO2 SF6 NO3- CH4 Na NaCl

Oxidation and Reduction A substance is oxidized if its oxidation number becomes more positive (loss of electrons) A substance is reduced if its oxidation number becomes more negative (gain of electrons) OIL RIG or LEO GER Oxidation and reduction are coupled reactions, if you have one, you must have the other

Examples For the following reactions, assign oxidation states and identify oxidized substance and reduced substance Ce+4(aq) + Sn+2(aq)  Ce+3(aq) + Sn+4(aq) CH4(g) + O2(g)  CO2(g) + H2O(g) 2 Al(s) + 3I2(s)  2AlI3(s) 2 PbS(s) + 3 O2(g)  2 PbO(s) + 2 SO2(g) PbO(s) + CO(g)  Pb(s) + CO2(g)

Redox Reactions For the following reactions, assign oxidation states and identify oxidized substance and reduced substance Cu + HNO3  CuNO3 + H2 H2 + O2  H2O Na + FeCl2  NaCl + Fe SiCl4(l) + Mg(s)  MgCl2(s) + Si(s) Reduced – O : O2 + 4 e-  2 H2O Oxidized – H : H2  H2O+ 2 e- => 2H2  2 H2O+ 4 e- Molecular eq: : 2 H2 + O2  2 H2O

Identifying Types of Reactions Characteristics of each type of reaction Precipitation Two (or more) aqueous ionic compounds Dead giveaway: One (or more) solid, insoluble, ionic product(s) Acid-Base Acid reacting with base Dead giveaway: formation of water Redox Transfer of electrons (write oxidation states) Dead giveaway: element in natural state forming a compound