Exam 3 Objectives: o Nomenclature m-nm, m(vos)-nm, nm-nm o Evidence for Chemical Reactions o Writing Chemical Equations o Balancing Chemical Equations o Classifying Chemical Reactions o Combination Reactions o Decomposition Reactions o Single-Replacement Reactions The Activity Series o Double-Replacement Reactions Solubility Rules o Neutralization Reactions H + + OH - H 2 O (l) Nomenclature 1
Evidence for a chemical Reactions There are four ways to tell if a chemical reaction has occurred: 1. A gas is produced. 2. An insoluble solid is produced. 3. A permanent color change is observed. 4. An energy change is observed. An exothermic reaction gives off heat and an endothermic reaction absorbs heat. 2
Diatomic Molecules Seven nonmetals occur naturally as diatomic molecules: 1. Hydrogen (H 2 ) 2. Nitrogen (N 2 ) 3. Oxygen (O 2 ) 4. Halogen (F 2 ) 5. Halogen (Cl 2 ) 6. Halogen (Br 2 ) 7. Halogen (I 2 ) These elements are written as diatomic molecules when they appear in chemical reactions. H 2 (g) N 2 (g) F 2 (g) O 2 (g) I 2 (s) Cl 2 (g) Br 2 (l) Have No Fear Of Ice Cold Beer Solid (s) Fe (s) Liquid (l) H 2 O (l) Gas (g) CO 2(g) Aqueous (aq) NaCl (aq) Aqueous means dissolved in water 3
reacts with, added to A Chemical Reaction produces, yields, gives A(s) + B(aq) C (l) + D (g) + E (aq) solid aqueous liquid gas Balancing Chemical Eqs When we balance a chemical equation, the number of each type of atom must be the same on both the product and reactant sides of the equation. We use coefficients in front of compounds to balance chemical reactions. Never change the subscripts P + I 2 PI 3 P + 3/2 I 2 PI 3 x2 2P + 3 I 2 2 PI 3 2P 6I 2P 6I 4
Practice: Balancing Chemical Eqs Classifying Chemical Reactions We can place chemical reactions into five categories: Synthesis rxs Decomposition rxs Oxidation Reduction rxs Precipitation rxs Acid-base rxs A + BC B + AC 5
Combination Reactions A combination reaction is a reaction in which simpler substances are combined into a more complex compound. Combination reactions are also called synthesis reactions. We will look at two combination reactions: 1. The reaction of a metal with nonmetal 2. The reaction of a nonmetal with nonmetal Reactions of Metals with Oxygen When a metal is heated with oxygen gas, a metal oxide is produced. metal + oxygen gas metal oxide For example, magnesium metal produces magnesium oxide. 6
Reactions of Nonmetals with Oxygen Oxygen and a nonmetal react to produce a nonmetal oxide. nonmetal + oxygen gas nonmetal oxide Sulfur reacts with oxygen to produce sulfur dioxide gas. S(s) + O 2 (g) SO 2 (g) Metal and Nonmetal Reactions A metal and a nonmetal react in a combination reaction to give an ionic compound. metal + nonmetal ionic compound Lithium reacts with bromine gas to produce lithium bromide. 2 Li(s) + Br 2 (g) 2 LiBr(s) When a main group (group I & II) metal reacts with a nonmetal, the formula of the ionic compound is predictable. If the compound contains a transition metal, the formula is not predictable. 7
Decomposition Reactions Occurs when a compound is broken down into simpler substances. Ex: Electrolysis of water 2H 2 O(l) 2H 2 (g) + O 2 (g) E=+1.23v Ex: Carbonates will decompose when heated Combination/decomposition summary In combination reactions, two or more smaller molecules are combined into a more complex molecule. In a decomposition reaction, a molecule breaks apart into two or more simpler molecules. 8
Single-Replacement Reactions A single-replacement reaction is a reaction in which a more active metal displaces another less active metal in a compound. If a metal precedes another in the activity series, it will undergo a single-replacement reaction. A + BC B + AC Fe(s) + CuSO 4 (aq) FeSO 4 (aq) + Cu(s) Double-Replacement Reactions In a double-replacement reaction, two ionic compounds in aqueous solution switch anions and produce an insoluble substance. AX + BZ AZ + BX If either AZ or BX is an insoluble compound, a precipitate will appear and there is a chemical reaction. If no precipitate is formed, there is no reaction. 9
Neutralization Reactions A neutralization reaction is the reaction of an acid and a base. HX + BOH BX + HOH A neutralization reaction produces a salt and water. H 2 SO 4 (aq) + 2 KOH(aq) K 2 SO 4 (aq) + 2 H 2 O(l) Classify the following Reactions 10
Predicting whether a reaction will occur In a single-replacement reaction, a more active metal displaces a less active metal according to the activity series. In a double-replacement reaction, two aqueous solutions produce a precipitate of an insoluble compound. The insoluble compound can be predicted based on the solubility rules. Single-Replacement: Activity Series More active will react! Li > K > Ba > Sr > Ca > Na > Mg > Al > Mn > Zn > Fe > Cd > Co > Ni > Sn > Pb > (H) > Cu > Ag > Hg > Au Mg > Cd so it WILL react! Mg (s) + CdCl 2(aq) MgCl 2(aq) + Cd (s) The MORE active metal wants to be in a compound!! 11
Double-Replacement Reactions, Continued Aqueous barium chloride reacts with aqueous potassium chromate as follows: BaCl 2 (aq) + K 2 CrO 4 (aq) BaCrO 4 (s) + 2 KCl(aq) From the solubility rules, BaCrO 4 is insoluble, so there is a double-replacement reaction. Aqueous sodium chloride reacts with aqueous lithium nitrate as follows: NaCl(aq) + LiNO 3 (aq) NaNO 3 (aq) + LiCl(aq) Both NaNO 3 and LiCl are soluble, so there is no reaction. Practice problems Write M.E., C.I.E., and N.I.E. for each of the following reactions. 1) potassium phosphate with copper (II) acetate 2) sodium sulfide with iron (III) nitrate 3) cesium hydroxide and oxalic acid 4) nickel (III) chloride and lead (II) nitrate 5) chromium (II) bromide with lithium oxalate 6) sulfuric acid with rubidium hydroxide 12
Practice problems Write M.E., C.I.E., and N.I.E. for each of the following reactions. 7) barium hydroxide with perchloric acid 8) cesium chromate with rubidium oxide 9) sodium fluoride with nickel (III) sulfate 10) antimony (V) carbonate reacts with sulfuric acid to form antimony (V) sulfate, carbon dioxide, and water 11) acetic acid with zinc hydroxide 13