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Type of Reactions Chemical reactions are classified into several general types Combination (Synthesis) Decomposition Single Replacement Double Replacement (Metathesis) 1 Combination (Synthesis) Two or more elements or simple compounds combine to form (synthesize) one product A + B AB 2Mg + O2 2MgO 2Na + Cl2 2NaCl SO3 + H2O H2SO4 2 Decomposition One substance is broken down (split) into two or more simpler substances. AB A + B 2HgO 2Hg + O2 2KClO3 2KCl + 3 O2 3 Learning Check R1 Classify the following reactions as 1) combination or 2) decomposition: ___A. H2 + Br2 2HBr ___B. Al2(CO3)3 Al2O3 + 3CO2 ___C. 4 Al + 3C Al4C3 4 Solution R1 Classify the following reactions as 1) combination or 2) decomposition: _1_A. H2 + Br2 2HBr _2_B. Al2(CO3)3 Al2O3 + 3CO2 _1_C. 4 Al + 3C Al4C3 5 Single Replacement One element takes the place of an element in a reacting compound. A + BC AB + C Zn + 2HCl ZnCl2 + H2 Fe + CuSO4 FeSO4 + Cu 6 Double Replacement Two elements in reactants take the place of each other AB + CD AD + CB AgNO3 + NaCl AgCl + NaNO3 ZnS ZnCl2 + H2S + 2HCl 7 Learning Check R2 Classify the following reactions as 1) single replacement 2) double replacement __A. 2Al + 3H2SO4 Al2(SO4)3 + 3H2 __B. Na2SO4 + 2AgNO3 Ag2SO4 + 2NaNO3 __C. 3C + Fe2O3 2Fe + 3CO 8 Solution R2 Classify the following reactions as 1) single replacement 2) double replacement 1_A. 2Al + 3H2SO4 Al2(SO4)3 + 3H2 2_B. Na2SO4 + 2AgNO3 Ag2SO4 + 2NaNO3 1_C. 3C + Fe2O3 2Fe + 3CO 9 Combustion A reaction in which a compound (often carbon) reacts with oxygen C + O2 CO2 CH4 + 2O2 CO2 + 2H2O C3H8 + 5O2 3CO2 + 4H2O C6H12O6 + 6O2 6CO2 + 6H2O 10 Learning Check R3 Balance the combustion equation ___C5H12 + ___O2 ___CO2 + ___H2O 11 Solution R3 Balance the combustion equation 1 C5H12 + 8 O2 5 CO2 + 6 H2O 12 Oxidation and Reduction Reactions that involve a loss or gain of electrons Occurs in many of the types of reactions and combustion Important in food metabolism, batteries, rusting of metals 13 Requirements for OxidizationReduction Electrons are transferred Two processes occur Oxidation = Loss of electrons (LEO) Zn Zn2+ + 2e- Reduction = Gain of electrons (GER) Cu2+ + 2e- Cu 14 Balanced Red-Ox Equations Combine the oxidation and reduction reactions to make Loss of electrons = Gain of electrons Zn + Cu2+ + 2e- Zn2+ + 2e- + Cu Zn + Cu2+ Zn2+ + Cu 15 Learning Check R3 Identify the following as an 1) oxidation or a reduction process: __A. Sn Sn4+ + 4e- __B. Fe3+ + 1e- Fe2+ __C. Cl2 + 2e- 2Cl- 16 Solution R3 Identify the following as an 1) oxidation or a reduction process: 1_ A. Sn Sn4+ + 4e- 2_ B. Fe3+ + 1e- Fe2+ 2_ C. Cl2 + 2e- 2Cl- 17 Redox • REDOX stands for REDuction/OXidation • Oxidation refers to a loss of electrons • Reduction refers to a gain of electrons • • • • • • LEO –GER Loss Electrons = Oxidation Gain Electrons = Reduction OIL-RIG Oxidation Is Loss Reduction Is Gain 18 oxidation = loss of e– X X+ + e– reduction = gain of e– X + e– X– 19 Oxidation numbers • We will see that there is a simple way to keep track of oxidation and reduction • This is done via “oxidation numbers” • An oxidation number is the charge an atom would have if electrons in its bonds belonged completely to the more electronegative atom 20 Rules 1. Any element, when not combined with atoms of a different element, has an oxidation # of zero. (O in O2 is zero) 2. Any simple monatomic ion (one-atom ion) has an oxidation number equal to its charge (Na+ is +1, O2– is –2) 3. The sum of the oxidation numbers of all of the atoms in a formula must equal the charge written for the formula. (if the oxidation number of O is –2, then in CO32– the oxidation number of C is +4) 21 Rules 4. In compounds, the oxidation # of IA metals is +1, IIA is +2, and aluminum (in IIIA) is +3 5. In ionic compounds, the oxidation # of a nonmetal or polyatomic ion is equal to the charge of its associated ion. (CuCl2, Cl is –1) 6. F is always –1, O is always –2 (unless combined with F), H is usually +1 total +1 +5 -6 +2 +12 -14 -4 +6 -2 +1 -1 +2 +5 -8 Ox.# +1 +5 -2 +1 +6 -2 -2 +1 -2 +1 -1 +1 +5 -2 HNO 3 K2Cr2O7 C2H6O AgI H2PO4– 22 11.1 Writing Chemical Equations 23 11.2 Classifying Reactions – Combination Reactions • A combination reaction is a chemical change in which two or more substances react to form a single new substance. 24 11.2 Classifying Reactions – Decomposition Reactions • A decomposition reaction is a chemical change in which a single compound breaks down into two or more simpler products. 25 11.2 Classifying Reactions – Single-Replacement Reactions • A single-replacement reaction is a chemical change in which one element replaces a second element in a compound. 26 11.2 Classifying Reactions • The activity series of metals lists metals in order of decreasing reactivity. • Generally, the higher in the periodic table, the more reactive. 27 28 29 11.2 Classifying Reactions – Double-Replacement Reactions • A double-replacement reaction is a chemical change involving an exchange of positive ions between two compounds. 30 31 32 11.3 Predicting the Formation of a Precipitate 33 11.2 Classifying Reactions – Combustion Reactions • A combustion reaction is a chemical change in which an element or a compound reacts with oxygen, often producing energy in the form of heat and light. 34 11.3 Net Ionic Equations • A complete ionic equation is an equation that shows dissolved ionic compounds as dissociated free ions. 35 11.3 Net Ionic Equations • An ion that appears on both sides of an equation and is not directly involved in the reaction is called a spectator ion. • The net ionic equation is an equation for a reaction in solution that shows only those particles that are directly involved in the chemical change. 36 11.3 Net Ionic Equations – A net ionic equation shows only those particles involved in the reaction and is balanced with respect to both mass and charge. 37 11.3 Net Ionic Equations • Sodium ions and nitrate ions are not changed during the chemical reaction of silver nitrate and sodium chloride so the net ionic equation is 38 39 40 41 42 11.3 • Will a precipitate form when a sodium carbonate solution is mixed with a barium nitrate solution? 43 11.3 Predicting the Formation of a Precipitate • Sodium nitrate is soluble but barium carbonate is insoluble. The net ionic equation is 44