CHAPTER Describing Chemical Reactions Reactants Products. New substances produced The arrow means yields TYPES OF EQUATIONS.

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1 CHAPTER 11 Chemical Reactions 11.1 Describing Chemical Reactions Reactants Products New substances produced The arrow means yields Where do Chemical Reactions occur? Everywhere!!! In living organisms In Food. In the air. WRITING CHEMICAL EQUATIONS In a chemical equation, an arrow separates the formulas of the reactants (on the left) from the formulas of the products (on the right) TYPES OF EQUATIONS Word Equation: write the names of the reactants and products, not the formulas. Sodium chloride + potassium nitrate Skeleton Equation: only the formulas of the reactants and products are included. Information in EQUATIONS Physical State of substance: (s)= solid, (l) = liquid, (g) =gas. (aq) = aqueous Catalyst added: used to speed up a reaction, but not part of the reactants or products. Not used in a reaction!! (Written over the yield sign) Catalyst 1

2 Symbols in EQUATIONS (aq) dissolved in water Yields Reversible Reaction Δ means heat is added written over the arrow Symbols used in Equations Table 11.1 Page 323 TYPES OF EQUATIONS Balanced Equation: Shows the relative amounts of each substance in a chemical reaction. Coefficients in front of the chemical formulas. Ex.) CaCO 3 or Al 2 (SO 4 ) 3 BALANCING CHEMICAL EQUATIONS We use coefficients in front of formulas to balance equations 2H 2 + O 2 2H 2 O What does the coefficient mean? 2H 2 + O 2 2H 2 O O H H O = O H H H H O H H In a chemical reaction, the reactants are different than the products. In every balanced equation, each side of the equation has the same number of atoms of each element. Conservation of Mass 2

3 Rules for Balancing Equations 1.Determine the correct formula. 2. Write a skeleton equation. (Formulas only!) 3. Determine the number of atoms of each element on reactants and products side. 4. Balance elements one at a time with coefficients. 5.Make sure the number of atoms on each side of the equation are equal. 6. Put coefficients in lowest whole number ratio. Mg + HCl MgCl 2 + H 2 KCl + Na 2 O K 2 O + NaCl C 3 H 8 + O 2 CO 2 + H 2 O Rules for Balancing Equations PAGE 327 Hints: hydrogen and oxygen last Make odd amounts even 1. Al + FeO Al 2 O 3 + Fe 3. P + O 2 P 2 O 5 2. Fe 2 O 3 + H 2 Fe+ H 2 O 4. Al(NO 3 ) 3 + H 2 SO 4 Al 2 (SO 4 ) 3 + HNO 3 3

4 5. CO 2 + H 2 O C 6 H 12 O 6 + O TYPES OF CHEMICAL REACTIONS 6. FeCl 3 + NaOH Fe(OH) 3 + NaCl You can be certain what the products of a chemical reaction are only by carrying out that reaction in the laboratory. 5 Reaction Types Combination (Synthesis) Decomposition Single Replacement Double Replacement Combustion Combination Reactions Two or more substances react to form a single substance The product must be a compound! Element + Element Compound Nonmetal oxides + water acid Metal oxides + water base Element + Element 2H 2 + O 2 2H 2 O 2 Cl 2 2NaCl N 2 + 3H 2 2NH 3 Pb + O 2 PbO 2 Nonmetal Oxide vs Metal Oxides Metal Oxide: > Mg + O: > K + O: Non metal Oxide: > C + O: > S + O: 4

5 Non Metal Oxide + Water SO 3 + H 2 O H 2 SO 4 CO 2 + H 2 O H 2 CO 3 SO 2 + H 2 O H 2 SO 3 N 2 O 5 + H 2 O 2HNO 3 P 2 O 5 + H 2 O 2H 3 PO 4 Metal Oxide + Water CaO + H 2 O Ca(OH) 2 K 2 O + H 2 O 2KOH BaO + H 2 O Ba(OH) 2 Li 2 O + H 2 O 2LiOH Decomposition Reactions Decomposition A single compound is broken down into two or more products. Usually require energy. Difficult to predict! Binary compounds break down into it s elements. PbCl 4 Pb + 2Cl 2 2H 2 O 2H 2 + O 2 CaCO 3 CaO + CO 2 SINGLE REPLACEMENT REACTIONS Atoms of an element replace the atoms of a second element in a compound. Needed: An Activity Series of Metals (Table 11.2 on page 333.) Halogens replace halogens (Decrease down 7A) Based on Electronegativity. Sometimes there is no reaction because an element is not reactive enough. Li K Ca Na Mg Al Zn Fe Sn Pb H Cu Ag Au Pt Activity Series of Metals Lithium replaces everything below it. Al (s) + LiNO 3 (aq) No Reaction Al (s) + CuCl 2 (aq) AlCl 3 (aq) + Cu (s) Why is gold, silver, and platinum used in jewelry? 5

6 Single Replacement K + NaCl KCl Sn + NaCl No Reaction F 2 + NaCl NaF + Cl 2 Br 2 + NaCl No Reaction DOUBLE REPLACEMENT Involves an exchange of positive ions between two compounds in aqueous solution Usually between 2 ionic compounds in aqueous solution. Results in a gas, water, or a precipitate. DOUBLE REPLACEMENT KCl + MgO K 2 O + MgCl 2 NaNO 3 + CaSO 4 Na 2 SO 4 + Ca(NO 3 ) 2 COMBUSTION REACTIONS Hydrocarbon + oxygen= carbon dioxide + water > complete combustion > CH 4 + 2O 2 CO 2 + 2H 2 O + Heat Hydrocarbon + oxygen= carbon monoxide + water > incomplete combustion > CH 4 + 2O 2 CO + 2H 2 O + Heat Incomplete combustion occurs when there is not enough oxygen available during the reaction, which produces CO. Combustion 2C 4 H O 2 8CO H 2 O CH 4 + 2O 2 CO 2 + 2H 2 O C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O 6

7 PREDICTING THE PRODUCTS OF A CHEMICAL REACTION The number of elements and/or compounds reacting is a good indicator of possible reaction type and thus possible products See page for a summary of the 5 reaction types. PREDICTING THE PRODUCTS When forming ionic compounds, always break up the reactants into IONS, then form the new compound. Metal Non Metal Single & Double Replacement Combination with Metal oxides 5 Reaction Types Combination (Synthesis) Decomposition Single Replacement Double Replacement Combustion Predicting Combination Reactions Fe+ O 2 K 2 O + H 2 O SO 3 + H 2 O Predicting Decomposition Reactions Fe 2 O 3 NaCl Predicting Combustion Reactions CH 4 + O 2 C 2 H 6 + O 2 H 2 O 2 C 3 H 8 + O 2 7

8 Li K Ca Na Mg Al Zn Fe Sn Pb H Cu Ag Au Pt Activity Series of Metals Lithium replaces everything below it. Al (s) + LiNO 3 (aq) No Reaction Al (s) + CuCl 2 (aq) AlCl 3 (aq) + Cu (s) Why is gold, silver, and platinum used in jewelry? Predicting Single Replacement Reactions Zn + FeCl 3 F 2 + CaO K + HCl Fe + Li 3 N Predicting Double Replacement Reactions ZnO + AlCl 3 NaF + CaO Hydrogen as a metal: Mg + HCl Incomplete Combustion: CH 4 + O 2 KNO 3 + Al 2 (SO 4 ) 3 How do you know the charge? NaCl + Fe(OH) REACTIONS IN AQUEOUS SOLUTION (99% = Double Replacement) Complete ionic equation Net ionic equation Spectator ion Double Replacement reactions usually occur in water. 8

9 Ag + Reaction: NO3 Cl Ag + NO 3 Cl NO3 NO 3 Ag + NO3 Cl Cl NO 3 NO 3 Ionic Equation: AgNO 3 NaCl AgCl (s) Complete Ionic Equation Shows dissolved ionic compounds as dissociated free ions. Double Replacement reaction in aqueous solution AgNO 3 (aq) + NaCl (aq) AgCl (s) + NaNO 3 (aq) Ag + + NO Cl AgCl + + NO 3 AgCl forms a precipitate. + NO 3 remain dissolved in water and do not participate in the reaction. 1. DR: 2 Ionic Compounds 2. SR: single element + 1 Ionic compound 3. Combustion: (CH) + O 2 4. Decomposition: 1 reactant 5. Combination: a.) element + element b.) metal oxide + H 2 O c.)nonmetal oxide + H 2 O Spectator Ions An ion that appears on both sides of a complete ionic equation and is not directly involved in the reaction. The ions not forming the precipitate. Net Ionic Equation Shows only those particles involved in the reaction and is balanced with respect to both mass and charge. No spectator ions present. 9

10 BaCl 2 (aq) + Na 2 SO 4 (aq) What is the precipitate? Write the complete ionic equation. What are the spectator ions? What is the net ionic equation? BaSO 4 (s) + NaCl (aq) Predicting the Formation of a Precipitate You can predict the formation of a precipitate by using the general rules for solubility of ionic compounds. Solubility rules on pg These show which ions dissolve in water and which form precipitates. 1. DR: 2 Ionic Compounds 2. SR: single element + 1 Ionic compound 3. Combustion: (CH) + O 2 4. Decomposition: 1 reactant 5. Combination: a.) element + element b.) metal oxide + H 2 O c.)nonmetal oxide + H 2 O 10