Types of Chemical Reactions

States of Chemicals All chemicals will be one of the following states: Solid Liquid Gas Aqueous: Dissolved in water From now on, unless otherwise stated, assume that you are required to include the states for each chemical in any question

Hints for predicting states: 1. Read the question carefully! Often times the question will give away information regarding the states of many (if not all) chemicals involved Pay attention to the following terms: Precipitate = “solid” Soluble = “aqueous” 2. The states for individual elements are given on the periodic table On your table: look at the legend at the top of your table Regular font = solid Bold italic font = liquid Bubble letter font = gas

Hints for predicting states: 3: For compounds, make note of the following: Solids: Unless otherwise stated, most ionic compounds are solid at room temperature Gases: Common sense and life experience should remind you that compounds such as carbon dioxide and carbon monoxide are gases

Hints for predicting states: 3: For compounds, make note of the following: Liquids: Only pure, molecular (covalent) compounds can be found as liquids Alcohols and water are the only two we will come across Water is the most common one you will work with regularly Aqueous: Anything that is dissolved in water (read question & use common sense) All acids are always aqueous

Types of Chemical Reactions There are only five (5) different types of chemical reactions: 1) Double Replacement 2) Single Replacement 3) Synthesis/Formation 4) Decomposition 5) Combustion

Reaction Type 1 – Double Replacement Occur between two ionic compounds Does not happen with covalent compounds Involves an exchange of cations (positive ions) The cation of one compound trades places with the cation of another compound to form two new compounds

Identifying a Double Replacement Reaction Double replacement reactions always have two ionic compounds on the REACTANTS side AND on the PRODUCTS side of an equation *Two compounds react to form two new compounds* AB + CD  CB + AD A & C are cations, B & D are anions A & C switch places

Double Replacement - Characteristics occur in solution when the compounds are in an aqueous state (aq) reactants are either aqueous to begin with, or solid compounds dissolved in water to form an aqueous solution of ions Both reactants MUST be dissolved in water This allows the compounds to separate into their ions so that they can exchange/recombine in order to drive the reaction, one of the products must be removed from the aqueous solution this can occur via one of three ways:

Double Replacement - Characteristics 1) Formation of a precipitate (an insoluble solid forms in the solution) i.e.: Pb(NO3)2 (aq) + 2NaI (aq)  2NaNO3 (aq) + PbI2 (s) Solid lead (II) iodide is formed as precipitate and comes out of the solution

Double Replacement - Characteristics 2) Water is formed when a hydrogen cation unites with a hydroxide anion i.e.: NaOH (aq) + HCl (aq)  HOH (l) + NaCl (aq) Water (HOH) is formed and comes out of the solution

Double Replacement - Characteristics 3) Formation of a gas i.e.: FeS (aq) + 2HCl (aq)  H2S (g) + FeCl2 (aq) Hydrogen sulfide gas is formed and comes out of the solution

1) Formation of a Precipitate Determining if a Double Replacement Reaction Occurs & Predicting the States of the Products 1) Formation of a Precipitate Use a “Solubility Table” Look at the compounds formed, and use a solubility table to identify if a precipitate is formed Ion combination = “low solubility” A precipitate is formed, state will be written as a solid in the products Ion combination = “soluble” No precipitate forms, state will be written as aqueous. If both products are aqueous, NO REACTION OCCURS - You will simply have a mixture of ions

Determining if a Double Replacement Reaction Occurs & Predicting the States of the Products 2) Formation of water If water is a product, it will be written as a “liquid”, not “aqueous” since it is a pure liquid Yes, water is technically a covalent compound, however it is still present in double replacement reactions. It is created when an H+ cation combines with a OH- anion Sometimes it is helpful to write H2O as HOH symbolizing the joining of a H+ cation and an OH- anion 3) Formation of a gas Solubility table is not helpful More difficult to identify Use your best judgment, or the info will be given in the question

What if both products are aqueous? In this case, the reaction will NOT PROCEED or will NOT HAPPEN Remember, in order for a double replacement reaction to occur, one of the products MUST leave the solution – if both products stay in solution, no reaction occurs i.e. KCl (aq) + NH4CH3COO (aq)  KCH3COO (aq) + NH4Cl (aq) NO REACTION