Types of Chemical Reactions Synthesis (combination) reactions – two or more substances combine to form a single substance. A + B = AB Group A metals combine with nonmetals to form ionic compounds. (To get the correct formula you must know the charges of the cations and anions that the metal and nonmetal form). 2K(s) + Cl2(g) 2KCl(s) When two nonmetals react in a synthesis reaction, there is more than one possible product. – you must be given the product name S(s) + O2(g) SO2(g) or 2S(s) + 3O2 2SO3(g) When a transition metal and a nonmetal react in a synthesis reaction, there may be more than one possible product because the transition metal could form more than one cation. – you must be given at least the charge on the cation. Fe(s) + S(s) FeS(s) Iron (II) sulfide 2Fe(s) + 3S(s) Fe2S3 Iron (III) sulfide. Nonmetal oxides (nonmetal with oxygen) react with water to produce an acid (H+ compound). SO2(g) + H2O(l) H2SO3(aq) sulfurous acid Metallic oxides (metal with oxygen) react with water to give a base (OH- compounds). Use ionic charges to write formula of product. CaO(s) + H2O(l) Ca(OH)2(aq) A metal oxide and nonmetal oxide combine to form a salt. CO2(g) + Na2O(cr) Na2CO3(s) Decomposition Reactions – a single compound is broken down into two or more products and usually require energy (heat, light or electricity) to take place. AB A + B When a binary (2 elements only) compound breaks down, the products will be those 2 elements. electricity H2O(l) H2(g) + O2(g) . When some acids are heated, they decompose to form water and nonmetal oxide H2CO3(aq) CO2(g) + H2O(l) When some metal hydroxides (metal combined with OH-)are heated, they decompose to form a metallic oxide and water. Ca(OH)2 CaO(s) + H2O(g) 2- When some metallic carbonates (metal combined with CO3 ) are heated, they decompose to form a metallic oxide and carbon dioxide. Li2CO3(s) Li2O(s) + CO2(g) - When metallic chlorates (metal combined with ClO3 )are heated, they decompose to form metallic chlorides and oxygen. KClO3(s) 2KCl(s) + 3O2(g) Single Replacement/Displacement Reactions – one element replaces a second element in a compound. A + BC B + AC (If A is a metal) or A + BC C + BA (If A is a nonmetal) Whether one metal will displace another metal from a compound can be determined by the relative reactivities of the two metals. An activity series lists the reactivities of some metals. Activity Series of Metals Name Symbol Lithium Li Potassium K Calcium Ca Sodium Na Magnesium Mg Aluminum Al Zinc Zn Iron Fe Decreasing Reactivity Lead Pb (Hydrogen) (H)* Copper Cu Mercury Hg Silver Ag *Metals from Li to Na will replace H from acids and water; from Mg to Pb they will replace H from acids only. A nonmetal can also replace another nonmetal from a compound, usually a halogen. The activity of the halogens decreases as you go down group 17 of the periodic table. F Cl Br I At Combustion Reactions – an element or compound reacts with oxygen, often producing energy as heat and light. Commonly involves hydrocarbons (compounds that only contain H and C) . Complete combustion – forms carbon dioxide and water. CxHy + O2 CO2 + H2O . Incomplete combustion – reaction runs out of oxygen, then elemental carbon and carbon monoxide may be additional products. Combustion reactions between elements and oxygen also exist. 2Mg(s) + O2(g) 2MgO(s) Double Replacement/Displacement Reactions – Involve an exchange of two anions between two reacting ionic compounds. AB + CD AD + CB For a double- displacement reaction to occur, one of the following is usually true: 1. One product precipitates out of solution. 2. One product is a gas that bubbles out of the mixture. 3. One product is a molecular compound, usually water. To describe double displacement reactions more clearly we use net ionic equations. Net Ionic Equations Most ionic compounds when dissolved in water dissociate, or separate, into their anions and cations. Molecular equation: AgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq) 1+ 3- When AgNO3 is dissolved in water, it separates into Ag cations and NO anions. The other aqueous compounds dissociate also. Complete Ionic Equation: + - + - + - Ag (aq) + NO3 (aq) + Na (aq) + Cl (aq) AgCl(s) + Na (aq) + NO3 (aq) Ions that appear on both sides of the reaction are not directly involved in the reaction and are called spectator ions. These ions may be canceled out of the reaction. Net Ionic Equation: + - Ag (aq) + Cl (aq) AgCl(s) Note: When writing a balanced net ionic equation, you must balance the charges as well as the atoms. Precipitation Reactions The solid that forms after a reaction is called a precipitate. To decide if the product is a precipitate or not you must follow the solubility rules. Solubility Rules for Ionic Compounds Soluble Insoluble (dissolve, dissociate, separate) Stays a solid in solution - Nitrate (NO3 ) salts - Chlorate (ClO3 ) salts + + + Alkali metal salts (Na , K ) and ammonium salts (NH4 ) Chloride salts (Cl-) and Br-, I- Except ones with Ag, Hg, and Pb 2- Sulfate salts (SO4 ) Except ones with Pb, Ag, Hg, Ba, Sr, and Ca 2- Sulfides (S ) 3- Phosphates (PO4 ) 2- Chromates(CrO4 ) 2- Carbonates (CO3 ), Except ones with Na, K and Ca Hydroxides (OH-) *salt is used to mean ionic compound Acid/ Base Reactions/Neutralization Reactions Acids – a substance that produces H+ ions (protons) when it is dissolved in water. Strong acids completely dissociate in water. The strong acids are HCl, HNO3, and H2SO4. Bases/alkalis – a substance that produces hydroxide ions (OH-) in water. Strong bases completely dissociate in water. The strong bases are NaOH and KOH. In the reaction of a strong acid and a strong base, one product is always water and the other is always a salt (ionic compound) that remains dissolved in the water. Therefore, the net ionic equation for all strong acid/strong base reactions is always: + - H (aq) + OH (aq) H2O(l) Oxidation-Reduction (Redox) Equations – involves the transfer of electrons. Electrolyte – Carries a current through water. Strong – almost all of the molecules dissociate into ions, carries a strong current. Weak – some may dissociate, but mostly the molecule stays intact in water, carries very little current. Oxidation - Reduction Combustion Synthesis Decomposition Double displacement Single displacement Activity series Formation of metals of a gas Precipitation Acid/Base Activity Series of halogens .