Types of Chemical Reactions

About Chemical Reactions. . . REMEMBER a chemical reaction is a process through which a chemical change takes place -- chemical reactions start with one or more substances undergoing a chemical change to create new substances -- the original substance(s) is/are called the reactants -- the new substance(s) is/are called the products A chemical reaction will ALWAYS produce a new substance There are six different ways in which a new substance can be produced. . . -- these are the six types of chemical reactions

Type #1: Synthesis Reactions Synthesis reactions occur when 2 or more substances combine to form a larger, more complex compound -- also called a combination reaction -- also called an addition reaction THERE WILL ONLY BE 1 COMPOUND AS A PRODUCT Always follows the general equation: A + B AB +

Examples of Synthesis Reactions Example: Making Hydrochloric Acid (HCl) Hydrogen gas and chlorine gas react to form hydrochloric acid: H2 (g) + Cl2 (g) 2 HCl (l) How do you easily identify a synthesis reaction? -- Are there elements or simple (usually diatomic) compounds as reactants? -- Is there only 1 compound as a product? 2 Mg (s) + O2 (g) 2MgO (s)

Type #2: Decomposition Reactions Decomposition reactions are the opposite of synthesis reactions Large compounds break down into smaller compounds or elements THERE IS ALWAYS ONLY 1 REACTANT Always follow the general formula: AB A + B +

Examples of Decomposition Reactions Mg(ClO3)2 (s) MgCl2 (s) + 3O2 (g) Example: Breakdown of mercury (II) oxide Mercury (II) oxide decomposes to form liquid mercury and oxygen gas HgO (s) 2 Hg (l) + O2 (g) How do you easily identify a decomposition reaction? -- Is there only 1 compound for a reactant? -- Are there multiple elements or compounds as products? Mg(ClO3)2 (s) MgCl2 (s) + 3O2 (g)

Type #3: Single-Displacement Reactions In a single-displacement reaction, one element replaces another element in a compound -- a metal will always replace another metal -- hydrogen will always replace a metal -- a nonmetal will always replace a nonmetal These are also called single replacement reactions Always follows the general formula: A + BC AC + B + +

Examples of Single-Displacement Example: The single-displacement of zinc and hydrogen Aqueous hydrochloric acid reacts with zinc metal to form zinc chloride and hydrogen gas: Zn (s) + 2 HCl (aq) ZnCl2 (s) + H2 (g) Example 2: The single-displacement of chlorine and bromine Aqueous sodium bromide reacts with chlorine gas to form sodium chloride and liquid bromine Cl2 (g) + 2NaBr (aq) 2 NaCl (aq) + Br2 (l)

Type #4: Double-Displacement Rxns Also called double replacement reactions Always occurs between two ionic compounds, both of which are usually aqueous (solid dissolved in solution) -- the ions “switch partners” -- the cation of one compound partners with the anion of the other compound Always follows the general formula: AB + CD AD + CB + +

Requirements for Double-Displacement For a double-displacement reaction to occur: -- both reactants need to be ionic compounds -- one of the products must be insoluble Because double-displacement reactions happen between reactants that are aqueous ionic compounds, one of the products must no longer be aqueous Either: -- a precipitate will form -- a gas will form (bubbles will appear) -- water will be a product

Examples of Double-Displacement Example: Lead (II) nitrate and potassium iodide Aqueous lead (II) nitrate reacts with potassium iodide to form lead (II) iodide and potassium nitrate Pb(NO3)2 (aq) + KI (aq) PbI2 (s) + 2KNO3 (aq) Example #2: Barium and Potassium Aqueous barium chloride reacts with aqueous potassium carbonate to form barium carbonate and potassium chloride BaCl2 (aq) + K2CO3 (aq) BaCO3 (s) + 2KCl (aq)

Type #5: Combustion Reactions CxHy + O2 (g) CO2 (g) + H2O (l) + heat Combustion reactions are a special type of reaction which involve the burning of a hydrocarbon in oxygen gas -- the products are ALWAYS water and carbon dioxide -- heat is also given off as a byproduct Combustion reactions always follow the general formula: CxHy + O2 (g) CO2 (g) + H2O (l) + heat H H H + + H H H H H

Examples of Combustion Reactions Example: The burning of methane gas (Bunsen burner) Methane gas reacts with oxygen gas to form carbon dioxide, water, and heat CH4 (g) + 2 O2 (g) CO2 (g) + 2 H2O (l) + heat How do you easily identify a combustion reaction? -- look for a hydrocarbon and oxygen as reactants -- look for water and carbon dioxide as products C3H8 (g) + 5 O2 (g) 3 CO2 (g) + 4 H2O (l)

Type #6: Acid-Base Reactions HBr (aq) + KOH (aq) KBr (aq) + H2O (l) Acid-base reactions are a special type of double-displacement reaction where a hydrogen cation in one reactant and a hydroxide anion in the other reactant combine to form water as a product: Example: The neutralization of hydrogen bromide with potassium hydroxide Hydrogen bromide (hydrobromic acid) reacts with potassium hydroxide (a base) to form potassium bromide (a salt) and water HBr (aq) + KOH (aq) KBr (aq) + H2O (l)

Identifying Acid-Base Reactions How do you easily identify acid-base reactions? -- look for a basic double-displacement reaction -- look for the hydroxide ion in the reactants (OH) -- look for water as a product

Identify the Following Reaction Types 2CH3OH (l) + 3 O2 (g) 3 CO2 (g) + 4 H2O (l) FeS (aq) + 2 HCl (aq) H2S (aq) + FeCl2 (s) PbO2 (s) Pb (s) + O2 (g) Cl2 (g) + 2 NaI (s) 2 NaCl (s) + I2 (g) SO2 (s) + H2O (l) H2SO3 (aq)