Unit IV: Chemical Equations & Stoichiometry A. The chemical equation B. Types of chemical reactions A. Activity series of metals B. Solubility rules C. Rules for writing and balancing equations D. Calculations from chemical equations E. Limiting reactant F. Applications of stoichiometry G. Theoretical and percent yeild
4-A The Chemical Equation Word equations: Solid potassium chlorate, when heated, decomposes to produce solid potassium chloride and oxygen gas. Chemical equation: 2 KClO 3(s) 2KCl (s) + 3 O 2(g)
The Chemical Equation Convert the following word equations into a chemical equation: Aqueous silver nitrate reacts with aqueous strontium chloride to form a silver chloride precipitate and a solution of aqueous strontium nitrate. Solid iron (III) oxide and aluminum powder are heated and react to form solid aluminum oxide and liquid iron.
Classes of Chemical Reactions Combination Decomposition Single Replacement Double Replacement Neutralization Combustion
Evidence for a Chemical Change Heat being released (exothermic) or absorbed (endothermic) Light is given off Color change Evolution of gas Precipitate forms when solutions are mixed Formation of new substances
Combination (synthesis) Reaction General form of combination reaction A + B C Ex. Iron and oxygen 2Fe (s) + 3O 2(g) 2Fe 2 O 3(s)
Decomposition Reaction General form of the equation AB A + B An example would be nitrogen triiodide 2 NI 3 (s) N 2 (g) + 3 I 2 (g) Demonstration
Single Replacement A + BD AD + B Reaction Here A represents a metal, B a metal ion and D an anion. If A is more active than B it will replace it. Ex. Aluminum + Iron (III) oxide Demonstration
Activity series Most Reactive Mg 2+ Mg Mg Al Al 3+ Zn Zn Fe Fe Ni Ni 2+ Sn Sn Pb Pb Zn 2+ Fe 2+ Sn 2+ Pb 2+ H 2(g) 2H + (aq) Cu Cu Ag Ag + Hg Hg Au Au Cu 2+ Least Reactive Hg 2+ Au 3+
Double Replacement Reaction General form of the equation AB + CD AD + CB The cation and anion of one compound switch with those of another Ex. Mercury (II) chloride and sodium iodide Demonstration
Solubility Rules All compounds with Group IA or NH4 + cations are soluble in water All compounds with nitrate and acetate anions are soluble in water All halides (F -, Cl -, Br -, I - ) are soluble except in compounds with Ag +, Pb 2+, Hg 2+ 2 All sulfates are soluble except with Ba 2+, Sr 2+, Ca 2+, and Pb 2+ See the Table on page 109 of your manual for a more complete list of some solubility rules
Combustion Reaction General equation: Hydrocarbon + O 2 CO 2 + H 2 O The oxygen can come from a variety of sources Ex. Oxidation of glycerin 14 KMnO 4 + 4 C 3 H 5 (OH) 3 7 7 K 2 CO 3 + 7 Mn 2 O 3 + 5 CO 2 + 16 H 2 O Demonstration
Lecture Problems 4-1 pg. 111 Write complete chemical equations for the following and include their classification a. Al (s) + O 2 (g) aluminum oxide b. ammonia gas hydrogen gas + nitrogen gas c. C 6 H 12 (l) + oxygen gas CO 2 (g) + H 2 O (g) d. (NH 4 ) 2 SO 4 (aq) + BaCl 2 (aq) barium sulfate (s) + ammonium chloride (aq) Extra practice: Al (s) + copper (II) sulfate (aq) copper (s) + aluminum sulfate (aq)
Rules for Balancing Equations 1.Write the correct formulas for reactants and products. 2.Count and compare the number of atoms of each element on both sides of the equation 3.Balance the elements one at a time, by using stoichiometric coefficients in front of the necessary compounds. Remember! Never change the actual formula of a compound to balance the equation
Rules for Balancing Equations 4. Start with the most complicated compound first. (The one with the most atoms) 5. Make sure as you work through each element you note any others that become unbalanced. 6. Try balancing oxygen and hydrogen last. 7. Polyatomic groups that are not changed during the reaction are balanced as groups. 8. The numbers used (stoichiometric coefficients) to balance an equation should be in the smallest ratio possible.
Lecture Problem IV-2 (pg. 113) a. Fe (s) + O 2(g) > Fe 2 O 3(s) Solid iron combines with oxygen gas to form solid iron (III) oxide. b. Mg (s) + N 2(g) > (s) Solid magnesium reacts with nitrogen gas to form solid magnesium nitride d. Co 2 (CO 3 ) 3(s) > Co 2 O 3(s) + CO 2(g) Solid cobalt (III) carbonate decomposes to form solid cobalt (III) oxide and carbon dioxide gas f. AgClO 3(s) > AgCl (s) + O 2(g) Solid silver chlorate decomposes to form solid silver chloride and oxygen gas
Lecture Problem IV-2 (pg. 114) h. Sn (s) + HCl (aq) > SnCl 2(aq) + H 2(g) Tin metal reacts with hydrochloric acid to form aqueous tin (II) Chloride and hydrogen gas. j. P 4(s) + N 2 O (g) > P 4 O 6(s) + N 2(g) Solid phosphorus reacts with dinitrogen monoxide to form solid Tetraphosphorus hexaoxide and nitrogen gas. l. Pb(C 2 H 3 O 2 ) 2(aq) + KI (aq) > (s) + KC 2 H 3 O 2(aq) Aqueous lead (II) acetate reacts with aqueous potassium iodide to form a solution of potassium acetate and a precipitate of lead (II) iodide. o. H 2 SO 4(aq) + KOH (aq) > K 2 SO 4(aq) + H 2 O (g) Sulfuric acid is neutralized with potassium hydroxide to form a solution of potassium sulfate.
Lecture Problem IV-2 (pg. 115) q. C 8 H 18(l) + O 2(g) > (g) + H 2 O (g) Liquid octane is burned in oxygen gas to form gaseous carbon dioxide and water vapor. r. NH 3(g) + O 2(g) > NO 2(g) + H 2 O (g) Gaseous ammonia reacts with oxygen to form nitrogen dioxide gas and gaseous water.
Extra Practice: Complete the Following Magnesium metal reacts with H 2 SO 4(aq) CH 3 (CH 2 ) 3 CH 2 OH + oxygen gas NaHCO 3 + HCl (aq) aqueous sodium chloride + water + carbon dioxide gas. Sulfur and oxygen combine when heated to form sulfur dioxide gas. MgCO 3 + heat MgO + AgNO 3(aq) + NaCl (aq)...