Answers and Solutions to Text Problems

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1 Chapter 6 Answers and Solutions 6 Answers and Solutions to Text Problems 6.1 A chemical change occurs when the atoms of the initial substances rearrange to form new substances. Chemical change is indicated by a change in properties of the reactants. For example, a rusting nail, souring milk, and a burning match are all chemical changes. a. physical: the shape changes, but not the substance. b. chemical: new substances form c. physical: water evaporates forming gaseous water d. chemical: the composition of the substances change to give new substances e. physical: water freezes f. chemical: new substances form 6.2 a. physical b. chemical c. physical d. chemical e. chemical f. physical 6.3 a. On the reactant side, there are two nitrogen atoms and four oxygen atoms. On the product side, there are two nitrogen atoms (2NO) and four oxygen atoms (2NO + O 2 ) b. On the reactant side, there are five carbon atoms (5C), two sulfur atoms (2SO 2 ), and four oxygen atoms (2SO 2 ). On the product side, there are five carbon atoms, two sulfur atoms, and four oxygen atoms c. On the reactant side, there are four carbon atoms, four hydrogen atoms, and ten oxygen atoms. On the product side, there are four carbon atoms, four hydrogen atoms, and ten oxygen atoms. d. On the reactant side, there are two nitrogen atoms, eight hydrogen atoms, and four oxygen atoms. On the product side, there are two nitrogen atoms, eight hydrogen atoms, and four oxygen atoms 6.4 a. On the reactant side, there are one carbon atom, four hydrogen atoms, and four oxygen atoms. On the product side, there are one carbon atom, four hydrogen atoms, and four oxygen atoms. b. On the reactant side, there are four phosphorus atoms, and ten oxygen atoms. On the product side, there are four phosphorus atoms, and ten oxygen atoms c. On the reactant side, there are ten nitrogen atoms, twelve hydrogen atoms, and six oxygen atoms. On the product side, there are ten nitrogen atoms, twelve hydrogen atoms, and six oxygen atoms. d. On the reactant side, there are six carbon atoms, eighteen oxygen atoms, and twelve hydrogen atoms. On the product side, there are six carbon atoms, eighteen oxygen atoms, and twelve hydrogen atoms 6.5 An equation is balanced when there are equal numbers of atoms of each element on the reactant as on the product side. a. not balanced b. balanced c. not balanced d. balanced 6.6 a. balanced b. balanced c. not balanced d. not balanced 6.7 a. There are two sodium atoms and two chlorine atoms on each side of the equation. b. There are three chlorine atoms, one phosphorus atom, and six hydrogen atoms on each side of the equation. c. There are four phosphorus atoms, sixteen oxygen atoms, and twelve hydrogen atoms on each side of the equation.

2 Chemical Reactions 6.8 a. There are four nitrogen atoms and six oxygen atoms. b. There are two aluminum atoms, three oxygen atoms, six hydrogen atoms, and six chlorine atoms. c. There are five carbon atoms, twelve hydrogen atoms, and sixteen oxygen atoms. 6.9 Place coefficients in front of formulas until you make the atoms of each element equal on each side of the equation. Try starting with the formula that has subscripts. a. N 2 + O 2 2NO b. 2HgO 2Hg + O 2 c. 4Fe + 3O 2 2Fe 2 O 3 d. 2Na + Cl 2 2NaCl e. 2Cu 2 O + O 2 4CuO 6.10 a. 2Al + 3Cl 2 2AlCl 3 b. P 4 + 5O 2 P 4 O 10 c. C 4 H 8 + 6O 2 4CO H 2 O d. Sb 2 S 3 + 6HCl 2SbCl 3 + 3H 2 S e. Fe 2 O 3 + 3C 2Fe + 3 CO 6.11 a. There are two NO 3 in the product. Balance by placing a 2 before AgNO 3. Mg + 2 AgNO 3 Mg(NO 3 ) Ag b. CuCO 3 CuO + CO 2 c. Start with the formula Al 2 (SO 4 ) 3. Balance the Al by writing 2 Al and balance the SO 4 2- by writing 3CuSO 4 + Al + 3CuSO 4 3Cu + Al 2 (SO 4 ) 3 d. Pb(NO 3 ) NaCl PbCl 2 + 2NaNO 3 e. 2 Al + 6 HCl 2 AlCl H a. Zn + H 2 SO 4 ZnSO 4 + H 2 b. 2Al + 3H 2 SO 4 Al 2 (SO 4 ) 3 + 3H 2 c. K 2 SO 4 + BaCl 2 BaSO 4 + 2KCl d. CaCO 3 CaO + CO 2 e. Al 2 (SO 4 ) 3 + 6KOH 2Al(OH) 3 + 3K 2 SO a. Decomposition. A single reactant splits into two simpler substances (elements). b. This is a single replacement reaction. I 2 in BaI 2 is replaced by Br a. Two elements unite to form a compound. b. The components in two reactants exchange places a. combination and combustion b. single replacement c. decomposition d. double replacement e. combustion f. decomposition g. double replacement h. combination and combustion 6.16 a. double replacement b. combination c. combustion d. double replacement e. combination and combustion f. single replacement g. decomposition h. double replacement 6.17 a. Combine the reactants to form a large compound: Mg + Cl 2 MgCl 2 b. Split the reactant to give simpler substances: 2 HBr H 2 + Br 2 c. Replace the Zn with Mg: Mg + Zn(NO 3 ) 2 Mg(NO 3 ) 2 + Zn d. Switch metals placing K + with NO 3 and Pb 2+ with S 2 : K 2 S + Pb(NO 3 ) 2 2KNO 3 + PbS e. Write the products CO 2 and H 2 O and balance: 2 C 2 H O 2 4 CO H 2 O

3 Chapter 6 Answers and Solutions 6.18 a. Ca + S CaS b. PbO 2 Pb + O 2 c. 2KI + Cl 2 2KCl + I 2 d. CuCl 2 + Na 2 S CuS + 2NaCl e. C 2 H 4 + 3O 2 2CO 2 + 2H 2 O 6.19 a. oxidation b. reduction c. oxidation d. reduction 6.20 a. oxidation b. reduction c. reduction d. oxidation 6.21 a. Zinc(Zn) is oxidized because it loses electrons to form Zn 2+ ; chlorine (Cl 2 ) is reduced b. Bromide ion (2Br - ) is oxidized to Br 0 2 ; chlorine (Cl 2 ) is reduced to 2 Cl - (gains electrons) c. Oxide ion (O 2-) is oxidized to O 0 2 (loses electrons); lead (II) ion Pb 2+ is reduced d. Sn 2+ ion is oxidized to Sn 4+ (loses electrons) ; Fe 3+ ion is reduced to Fe 2+ ( gains electrons) 6.22 a. Lithium is oxidized and fluorine is reduced b. Iodide ion is oxidized and chlorine is reduced c. Zinc is oxidized and copper (II) ion is reduced d. Iron is oxidized and copper (II) ion is reduced 6.23 a. Fe 3+ + e - Fe 2+ is a reduction. b. Fe 2+ Fe 3+ + e is an oxidation For chlorine to become chloride ion, each chlorine atom must gain an electron: Cl 2 + 2e 2Cl Thus the reaction is a reduction Because the linoleic acid adds hydrogen, the acid has been reduced a. Because the reaction of succinic acid involves the loss of hydrogen, the acid is oxidized. b. Because the reaction of the coenzyme FAD involves the addition of hydrogen, the coenzyme is reduced. c. Because an oxidation always accompanies a reduction, one would expect the reaction of succinic acid to occur along with the FAD reaction. d. Energy reactants products Reaction progress 6.28 a. The heat of reaction is the heat energy that is given off (or used up) during a reaction as a result of reactant(s) bonds being broken and product(s) bonds being formed. b. In an exothermic reaction, energy is given off because the products are lower in energy than the reactants. In an endothermic reaction, energy is absorbed in forming products with a higher energy than the reactants. c. Because energy is absorbed during an endothermic reaction, the products have a higher energy than the reactants. d. Energy products Energy of activation reactants Reaction progress

4 Chemical Reactions 6.29 a. exothermic; heat loss b. endothermic; heat gain c. exothermic; heat loss 6.30 a. The reaction is exothermic. b. The reaction is endothermic. c. The reaction is endothermic a. exothermic b. endothermic c. exothermic 6.32 a. The reaction is exothermic. b. The reaction is exothermic. c. The reaction is endothermic a. The rate of a reaction relates the speed at which reactants are transformed into products. b. Because more reactants will have the energy necessary to proceed to products, (the activation energy), at room temperature than at refrigerator temperatures, the rate of formation of mold will be higher at room temperature a. A catalyst provides an alternate reaction pathway with a lower activation energy, and thus more reactants will have the energy necessary to form products. This results in an increased rate of reaction. b. The use of pure oxygen increases the amount of reactant present, increasing the rate of oxygenation of hemoglobin in blood a. Addition of a reactant increases the reaction rate. b. Increasing the temperature increases the number of collisions with the energy of activation. The rate of reaction will be increased. c. Addition of a catalyst increases the reaction rate. d. Removal of reactant decreases the reaction rate a. Addition of a reactant increases the reaction rate. b. Lowering the temperature decreases the number of reactant molecules with the energy necessary for reaction to occur, (activation energy). The rate of reaction will be decreased. c. Removing reactant decreases the reaction rate. d. Addition of a catalyst increases the reaction rate In a reversible reaction, the forward reaction converts reactants to products and a reverse reaction converts products back to reactants again A reversible reaction reaches equilibrium when the rate of the forward reaction is equal to the rate of the reverse reaction, and the amounts of each species present remain constant a. Addition of a reactant pushes the reaction toward the product side. b. Addition of heat to an exothermic reaction pushes the reaction toward the reactant side. c. Removal of a product pulls the reaction toward the product side. d. Removal of a reactant pulls the reaction toward the reactant side a. Removal of a reactant pulls the reaction toward the reactant side in an attempt to reestablish b. Removing heat from an exothermic reaction pulls the reaction toward the product side in an attempt to re-establish c. Addition of a product pushes the reaction toward the reactant side in an attempt to reestablish d. Addition of a reactant pushes the reaction toward the product side in an attempt to reestablish

5 Chapter 6 Answers and Solutions 6.41 a. Addition of a reactant pushes the reaction toward the product side. b. Addition of a product pushes the reaction toward the reactant side. c. Addition of heat to an endothermic reaction pushes the reaction toward the product side. d. Removal of heat from an endothermic reaction pulls the reaction to the reactant side a. Addition of heat to an endothermic reaction pushes the reaction toward the product side in an attempt to re-establish b. Removal of heat from an endothermic reaction shifts the reaction toward the reactant side in an attempt to re-establish c. Removal of CO, which is a product, shifts the reaction toward the product side in an attempt to re-establish d. Addition of a reactant pushes the reaction toward the product side in an attempt to reestablish 6.43 As gaseous carbon dioxide escapes into the atmosphere, product is removed from the reaction system. According to LeChatelier s principle, the reaction will shift toward the product side in an attempt to re-establish However, the soda is open to the atmosphere and will continue to lose its carbonation More reactants must be consumed for the forward reaction s rate to increase. Because we obtain the reactant oxygen by breathing, our breathing rate must also increase a. 2Al + 3Cl 2 2AlCl 3 combination b. 2Fe + 3H 2 SO 4 Fe 2 (SO 4 ) H 2 single replacement c. 2AgNO 3 + H 2 S Ag 2 S + 2 HNO 3 double replacement d. Cl 2 + 2KI 2KCl + I 2 single replacement 6.46 a. 2NI 3 N 2 + 3I 2 decomposition b. 3Mg + N 2 Mg 3 N 2 combination c. 3Na 2 SO 4 + 2Al(OH) 3 Al 2 (SO 4 ) 3 + 6NaOH double replacement d. 2Fe + 6HCl 2FeCl 3 + 3H 2 single replacement 6.47 a. C 4 H O 2 4 CO H 2 O b. C 5 H O 2 5 CO H 2 O c. C 6 H 12 O O 2 6 CO H 2 O 6.48 a. 2C 2 H 6 + 7O 2 4CO 2 + 6H 2 O b. 2C 6 H 6 + 9O 2 6CO 2 + 6H 2 O c. 2C 3 H 8 O 3 + 7O 2 6CO 2 + 8H 2 O 6.49 a. Zn e Zn reduction b. Al Al e oxidation c. Pb Pb e oxidation d. Cl 2 + 2e 2Cl - reduction 6.50 a. S + Cl 2 SCl 2 b. Cl 2 + 2NaBr Br 2 + 2NaCl c. 2Al + Fe 2 O 3 Al 2 O 3 + 2Fe d. 2CuO + C 2Cu + CO a. S S e S oxidized; Cl 2 + 2e 2Cl Cl 2 reduced b. Cl 2 + 2e 2Cl Cl 2 reduced; 2Br Br 2 + 2e Br oxidized c. Al Al e Al oxidized; Fe e Fe Fe 3+ reduced d. Cu e Cu Cu 2+ reduced; C C e C oxidized

6 Chemical Reactions 6.52 Although gas will burn in the atmosphere, (as we have all seen in the lab and when using a gas stove), the activation energy must be provided to initiate the reaction. The energy provided by a lit match or by a spark is sufficient to initiate the combustion of gas N 2 (g) + 2O 2 (g) + heat 2NO 2 (g) a. Addition of heat will push the reaction to the right, which favors the formation of product, NO 2. b. Removal of N 2 will pull the reaction to the left, forming more reactants. c. Addition of O 2 will push the reaction to the right, forming more NO 2 product. d. Removal of NO 2 would pull the reaction to the right, which forms more NO 2 product. e. Removing heat favors the reaction to the left, which forms more reactants A high activation energy would be difficult to attain, except for just a few of the reactants present, and the reaction would therefore be slow An increase in hemoglobin molecules pushes the reaction towards the products, which provides more oxygenated hemoglobin in the blood C 2 H 6 O + 3O 2 2CO 2 + 3H 2 O a. Addition of reactant(s) would increase the rate of reaction. b. Addition of a catalyst would also increase the rate of reaction.