CHEM 1413 Chapter 6 Hmewrk Questins TEXTBOOK HOMEWORK 6.25 A 27.7-g sample f the radiatr clant ethylene glycl releases 688 J f heat. What was the initial temperature f the sample if the final temperature is 32.5 C (C s = 2.42 J/g- C) fr Ethylene Glycl. 6.55 Cpper(I) xide can be xidized t cpper(ii) xide: Cu 2 O(s) + (1/2)O 2 (g) 2CuO(s) H rxn = -146.0 kj Given H f = -168.6 kj/ml fr Cu 2 O(s), find H f f CuO(s) 6.67 Reactin f gaseus ClF with F 2 yields liquid ClF 3, an imprtant flurinating agent. Use the fllwing thermchemical equatins t calculate Hrxn fr this reactin: (1) 2 ClF(g) + O 2 (g) Cl 2 O(g) + OF 2 (g) H rxn = 167.5 kj (2) 2 F 2 (g) + O 2 (g) 2 OF 2 (g) H rxn = -43.5 kj (3) 2 ClF 3 (l) + 2 O 2 (g) Cl 2 O(g) + 3 OF 2 (g) H rxn = 394.1 kj 6.68 Silver brmide is used t cat rdinary black-and-white phtgraphic film, while high-speed film uses silver idide. (a) When 50.0 ml f 5.0 g/l AgNO3 is added t a cffee-cup calrimeter cntaining 50.0 ml f 5.0 g/l NaI, with bth slutins at 25 C, what mass f AgI frms? (b) Use Appendix B t find H rxn. (c) What is T sln [assuming the vlumes are additive and the slutin has the density (1.00 g/ml) and specific heat capacity (4.18 J/g- C) f water]? 6.74 Kersene, a cmmn space-heater fuel, is a mixture f hydrcarbns whse average frmula is C 12 H 26. (a) Write a balanced equatin, using the simplest whle-number cefficients, fr the cmplete cmbustin f kersene t gases.
(b) If Hrxn = -1.50x10 4 kj fr the cmbustin equatin as written in part (a), determine H f f kersene. (c) Calculate the heat released by cmbustin f 0.50 gal f kersene (d f kersene = 0.749 g/ml). (d) Hw many gallns f kersene must be burned fr a kersene furnace t prduce 1250 Btu (1 Btu = 1.055 kj)? 6.79 Use the fllwing infrmatin t find H f f gaseus HCl: (1) N 2 (g) + 3 H 2 (g) 2 NH 3 (g) H rxn = -91.8 kj (2) N 2 (g) + 4 H 2 (g) + Cl 2 (g) 2 NH 4 Cl(s) H rxn = -628.8 kj kj (3) NH 3 (g) + HCl(g) NH 4 Cl(s) H rxn = -176.2 kj 6.83 Liquid methanl (CH 3 OH) can be used as an alternative fuel in pickup and SUV engines. An industrial methd fr preparing it invlves the catalytic hydrgenatin f carbn mnxide: CO( g) + 2 H ( g) CH OH( l) 2 Catalyst 3 Hw much heat (in kj) is released when 15.0 L f CO at 85 C and 112 kpa reacts with 18.5 L f H 2 at 75 C and 744 trr? SUPPLEMENTARY HOMEWORK 1. A sample f a gas is expanded at a cnstant pressure f 700 trr frm a vlume f 3.0 gal t 7.0 gal. [1.0 gal = 3.79 L]. What is the wrk invlved in this expansin, in J [1 L-atm = 101 J]? 2. The cnstant vlume mlar heat capacity f methane, CH 4 (M=16.), is 33. J/ml- C. If 8.5 kj f heat is added at cnstant vlume t a 60. gram sample f CH 4, initially at 30 C, what is the final temperature f the sample? 3. The cnstant pressure heat capacity f prpane [C 3 H 8 (g), M=44] is 73.6 J/ml- C. A sample f prpane is at an initial temperature f 35.0 C. It is
fund that 12.4 kj f heat are required t raise the temperature f the sample t 78.5 C. Hw many grams f prpane are cntained in the sample? 4. Fr a prcess in which the internal energy des nt change, which f the fllwing are pssible? (i) heat>0,wrk<0 (ii) heat>0,wrk>0 (iii) heat<0,wrk<0 (iv) heat<0,wrk>0 (A) i and ii nly (B) iii and iv nly (C) ii and iv nly (D) ii and iii nly (E) i and iv nly (F) i and ii nly 5. A 96 g sample f methanl gas, CH 3 OH [M = 32.] is initially at 200 C and 700 trr. The sample is cled at cnstant pressure t 120 C. During this prcess, the vlume decreases frm 126. L t 105 L. The cnstant pressure mlar heat capacity f methanl is 52 J/ml- C. [1 l-atm = 101 J, 1 atm. = 760 trr] Calculate q, w and E fr this prcess, in kj. 6. A 110 g sample f prpane gas, CH 3 CH 2 CH 3 [M = 44.], is initially at 60 C in a 50 L cntainer. The gas is heated at cnstant vlume t 150 C. The cnstant vlume mlar heat capacity f prpane is 64 J/ml- C. Calculate q, w and E fr this prcess, in kj. 7. Cnsider the cmbustin f butane, 2 C 4 H 10 + 13 O 2 8 CO 2 (g) + 10 H 2 O(l) H = -5755. kj (a) What is the Enthalpy change assciated with the prductin f 140. grams f CO 2 (g) [M=44]? (b) What is the Enthalpy change assciated with frming 65. grams f C 4 H 10 [M=58] frm CO 2 and H 2 O? (c) Fr the cmbustin f a given sample f C 4 H 10, the Enthalpy change is -2500. kj. Hw many grams f H 2 O [M=18] were frmed?
Fr #8 - #9: The melting and biling pints f tluene, C 7 H 8 [M = 92.], are T m (r T f ) = -95 C, and T b = +111 C. The enthalpy f fusin is 6.6 kj/ml and the enthalpy f vaprizatin is 33.2 kj/ml. The cnstant pressure mlar heat capacities f the liquid and gas are 156 J/ml- C and 104 J/ml- C. 8. Calculate the heat invlved (in kj) in vaprizing 230 g f tluene at its biling pint (111 C), and heating the gas up t 200 C (at cnstant pressure). 9. Calculate the heat invlved (in kj) in cling 230 g f liquid tluene frm 80 C dwn t its freezing pint (-95 C) and crystallizing it t the slid phase. 10. Cnsider the reactin f ptassium with water: 2 K(s) + 2 H 2 O(l) 2 KOH(aq) + H 2 (g) H = -390 kj (a) If a 12. gram piece f ptassium (M=39.1) is drpped int 500 grams f water, initially at 26 C, what will be the final temperature f the water? The specific heat capacity f water is 4.18 J/g- C (b) If a 12. gram piece f ptassium (M=39.1) is drpped int a cntainer with a mixture f ice and liquid water (M=18) at 0 C), hw many grams f ice will melt? The mlar enthalpy f fusin f H 2 O is 6.0 kj/ml. 11. In an experiment t determine the Enthalpy f Slutin f KOH [M=56.1] in water, 4.0 grams f KOH was disslved in 100 grams f water initially at 26.0 C. It was fund that the temperature in the calrimeter warmed t 35.1 C. Determine the Enthalpy f Slutin f KOH (in kj/ml). Nte: The slutin's heat capacity was C sln = 450 J/ C.
12. Cnsider the reactin: 2 C 2 H 6 + 7 O 2 4 CO 2 + 6 H 2 O H = -3122 kj Which f the fllwing statements is/are incrrect?. i ii iii iv H fr frming ne mle f C 2 H 6 frm and CO 2 and H 2 O is -1561 kj H fr the cmbustin f 1.5 mles f C 2 H 6 is -2341 kj The enthalpy f frmatin f C 2 H 6 is +1561 kj/ml The enthalpy f frmatin f O 2 (g) is 0 kj/ml (A) iii nly (B) i & iii (C) ii & iii (D) i & ii 13. Which f the fllwing cmpunds wuld be the best fuel, based upn relative Fuel Values? (i) dimethylhydrazine, (CH 3 ) 2 NNH 2 M = 60. H cmb = -1694 kj/ml (ii) methanl, CH 3 OH (iii) ethanl, C 2 H 5 OH (iv) ctane, C 8 H 18 M = 32. H cmb = -726 kj/ml M = 46. H cmb = -1371 kj/ml M = 114. H cmb = -5500 kj/ml 14. The Fuel Value f glycerl, C 3 H 8 O 3 (M=92) is 18.0 kj/g. (a) What is the Enthalpy f Cmbustin ( H cmb ) f glycerl? (b) What is the enthalpy change fr the cmbustin f 40 grams f glycerl, in kj?