Let s writing NIE s for these reaction types, and answering questions about each. 3) Oxidation Reduction Reactions Single Displacement (aka Single Replacement) These may include the following reaction types: Single Displacement Addition (aka Combination aka Synthesis) Decomposition Combustion pp. 218, 220 One element reacts with a compound to produce a different element and a new compound. A+ BC AC + B if the element is a metal, it will replace the cation. A+ BC C+ BA if the element is a nonmetal, it will replace the anion. These are always redox; think about it. Fig. 8-15, p. 218 PREDICT THE PRODUCT 1. Ca + HCl 2. ZnBr 2 + I 2 3. Cu + AgNO 3 Answers are on the next slide. 1
ANSWERS: 1. Ca+ 2 HCl CaCl 2 + H 2 2. ZnBr 2 + I 2 ZnI 2 + Br 2 3. Cu+ 2AgNO 3 2Ag + Cu(NO 3 ) 2 Fig. 16-2, p. 459 Single-Replacement Redox Reactions A reaction occurs when a piece of zinc is dipped into a solution of copper (II) nitrate. Write the net ionic equations. Single-Replacement Redox Reactions Conventional (Molecular) Equation Zn (s) + Cu(NO 3 ) 2 (aq) Zn(NO 3 ) 2(aq) + Cu (s) Ionic Equation Zn (s) + Cu +2 (aq)+ NO 3 - (aq) Zn +2 (aq)+ NO 3 - (aq) + Cu (s) Net Ionic Equation Zn (s) + Cu +2 (aq) Zn +2 (aq)+ Cu (s) Fig. 9-9, p. 245 Single-Replacement Redox Reactions What happens if we place a piece of copper metal into a solution of zinc nitrate? Evidence shows that copper is below zinc on the Activity Series, therefore copper will not replace zinc and no reaction occurs. Cu (s) + Zn(NO 3 ) 2(aq) NR To predict the products of single-replacement reactions, we refer to the activity series. Is the free element above the element to be replaced in the compound? If yes, the reaction will occur Is the free element below the element to be replaced in the compound? If yes, then a reaction will NOT occur The more active an element is, the more likely it will form compounds! 2
Simple Activity Series of Metals K Ca Na Mg Decreasing Al Zn Fe Ni Pb H 2 Cu Ag Au Increasing Activity Series of Halogens Decreasing F 2 Cl 2 Br 2 I 2 Increasing Trends in Oxidation and Reduction Active metals: Lose electrons easily Are easily oxidized Active nonmetals: Gain electrons easily Are easily reduced On the exam, you will neverbe asked to write the equation for a reaction that would not happen. Magnesium turnings are added to a solution of iron(iii) chloride Therefore, we can postpone our consideration of the activity series until Chapter 18 (Electrochemistry) when we discuss Standard Reduction Potentials of Half-Reactions. Small chunks of solid lithium are added to water Chlorine gas is bubbled into a solution of sodium bromide 3
ADDITION REACTION aka SYNTHESIS aka COMBINATION A reaction in which two or more substances combine to form a single product. A +B + C ABC CaO(s) + SO 2 (g) CaSO 3 (s) Figure 4.14 Combination of Metal + Non-Metal : C (s) + O 2 (g) CO 2 (g) Aluminum reacts with oxygen gas DECOMPOSITION REACTION A reaction in which a single compound reacts to give two or more substances, usually requiring a raise in temperature. ABC A + B + C 2KClO 3 (s) 2KCl(s) + 3O 2 (g) Decomposition Reactions are often not spontaneous By heat Heating potassium perchlorate Electrolytic Decomposition Water 4
2H 2 O (l) 2H 2(g) + O 2(g) Figure 4.15 Decomposing a compound to its elements Fig. 8-13, p. 215 Decomposition versus Dissociation Dissociation: - a compound breaks apart into its component ions, usually as it dissolves in water. - considered a physical change since the substance retains its chemical identity, and can be fairly easily restored to its original state. Examples: NaCl Na + + Cl - HNO 3 H + + NO 3 - Decomposition: - a substance breaks down into to or more different substances. - considered a chemical change because the substance loses its chemical identity as the reverse reaction is unfavorable. Examples: (NH 4 ) 2 Cr 2 O 7 N 2 + 4H 2 O + Cr 2 O 3 2H 2 O 2 2H 2 O + O 2 COMBUSTION REACTION A reaction of a substance with oxygen, usually the rapid release of heat produces a flame. CH + O 2 CO 2 + H 2 O 2C 4 H 10 (g) + 13O 2 (g) 8CO 2 (g) + 10H 2 O(g) (hint: balance the C s first, followed by the H then the O s) Many times in a combustion reaction, heat energy is given off. In chemical terms this is called an exothermic reaction. The thermodynamic equation representing this exothermic reaction is: 2C 4 H 10 (g) + 13O 2 (g) 8CO 2 (g) + 10H 2 O(g) + heat (in Joules) GAS FORMATION REACTIONS A reaction that produces a gas from reactants not in the gaseous state. 2 HCl (aq)+ ZnS (s) ZnCl 2 (aq)+ H 2 S (g) Zn (s)+ 2 HCl (aq) ZnCl 2 (aq)+ H 2 (g) COMMON GAS FORMATION REACTIONS YOU SHOULD REMEMBER NH 4 OH NH 3 (g) + H 2 O (l) Many gas formation reactions involve two steps, first the double displacement reaction then the decomposition reaction of an unstable substance. H 2 CO 3 CO 2 (g) + H 2 O (l) H 2 SO 3 SO 2 (g) + H 2 O (l) Na 2 CO 3 + 2HCl 2 NaCl + H 2 CO 3 H 2 CO 3 CO 2 + H 2 O Besides carbonic acid (H 2 CO 3 ), sulfurous acid (H 2 SO 3 ) also decomposes into SO 2 and water. 5