What Is Required? You need to find the final temperature of an iron ring heated by burning alcohol g

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1 Calculatig Theral Eergy i a Bob Calorieter (Studet textbook page 309) 31. Predict the fial teperature of a g iro rig that is iitially at 25.0 C ad is heated by cobustig 4.95 g of ethaol, C 2 H 5 OH(l), i a ope syste; ΔH cob for ethaol is kj/ol. (Note: These are ot stadard coditios.) You eed to fid the fial teperature of a iro rig heated by burig alcohol. What Is Give? You kow the ass of iro: Fe = g You kow the iitial teperature of the iro: T iitial = 25.0ºC You kow the ass of ethaol bured: = 4.95 g C2H5OH You kow the heat of cobustio for ethaol: o H cob = kj/ol Pla Your Strategy Deterie the aout i oles,, of C 2 H 5 OH(l) cobusted usig the ass ad olar ass of ethaol ad the forula. Use the forula H H cob to calculate the heat give off durig cobustio. Sice E syste = E surroudigs, chage the sig of H to fid the aout of heat, Q, absorbed by the iro. Use the forula Q = c T to calculate the chage i teperature, T, of the iro. C2H5OH Act o Your Strategy 4.95 g = ol g /ol ol o H H cob ( ol )( kj/ ol ) kj J QH J Q ct J (5.00 g)(0.449 J/g C)( T ) J T (5.00 g )(0.449 J / g C) 590.7C 44 HR Cheistry 12 Solutios aual

2 Use T = T fial T iitial to deterie the fial teperature. T Tfial Tiitial Tfial TTiitial The fial 590.7C 25.00C 615.7C teperature of the iro is 616 C. Check Your Solutio The fial teperature ust be greater tha the iitial teperature sice heat is gaied by the iro. The aswer is reasoable sice a great deal of heat eergy was absorbed ad iro has a relatively low specific heat capacity. The fial teperature has the correct uber of sigificat digits. Uit 3 Part B HR 45

3 32. Calculate the olar ethalpy of cobustio of octae if 0.53 g of the fuel icreased the teperature of a coffee ca calorieter (13 g of aluiu ad L of water) by 17.2 C. Reeber to iclude the heat gaied by ot oly the water but also by the aluiu ca. You eed to calculate the olar ethalpy of cobustio for octae. What Is Give? You kow the ass of octae: C8H18 = 0.53 g You kow the ass of the aluiu ca: Al =13 g You kow the ass of water: = g You kow the chage i the teperature: T = 17.2 C You kow the specific heat capacity of Al(s): c Al = J/g C You kow the specific heat capacity of solutios is the sae as the specific heat capacity of H 2 O(l): c = 4.19 J/g C Pla Your Strategy Use the forula Q = c T to calculate the heat gaied by the aluiu ad the water. Sice E syste = E surroudigs, chage the sig of Q to fid the aout of heat, H, give off durig the cobustio. Deterie the aout i oles,, of C 8 H 18 (l) cobusted usig the ass ad olar ass of octae ad the forula C 8H18. Act o Your Strategy Q ( ct ) ( ct ) Al (13 g )(0.897 J/ g C )(17.2 C ) 2 ( g )(4.19 J/ g C J J J kj H Q kj 0.53 g g /ol ol )(17.2 C ) 46 HR Cheistry 12 Solutios aual

4 H Use the forulahcob to calculate the theral eergy released. H H cob cob H kj ol kj/ol The ethalpy of cobustio of octae is kj/ol. Check Your Solutio The ethalpy of cobustio is egative as expected sice heat is give off. The result is lower tha the value i Table 5.4 (studet textbook page 295) because i this experietal situatio, heat would be lost to the surroudigs. The aswer has the correct uber of sigificat digits. Uit 3 Part B HR 47

5 33. How uch propae (i gras) would have to be cobusted i a ope syste to icrease the teperature of L of water fro C to its boilig poit? (The olar ethalpy of cobustio of propae ca be foud i Table 5.4 o page 295 of the studet textbook.) You eed to deterie the ass of propae that will icrease the teperature of a saple of water to its boilig poit. What Is Give? You kow the volue of water: You kow the ass of water: V = L = g You kow the iitial teperature: T iitial = 20.00ºC You kow the fial teperature: T fial = C You kow the cheical forula for propae(g): C 3 H 8 You kow the olar ethalpy of cobustio for C 3 H 8 (g): You kow the specific heat capacity of H 2 O(l): c o H cob = kj/ol = 4.19 J/g C Pla Your Strategy Use the forula T = T fial T iitial to deterie the chage i teperature. Use the forula Q = c T to calculate aout of heat, Q, absorbed by the water. Sice E syste = E surroudigs, chage the sig of Q to deterie the aout of heat, H, give off durig the cobustio. o H Use the forula Hcob to deterie the aout i oles,, of C 3 H 8 (g). Act o Your Strategy T Tfial Tiitial C 20.00C 80.00C Q ct 2 ( g )(4.19 J/ g C )(80.00 C ) J kj H Q kj o H Hcob kj kj/ol C3H8 C3H kj kj /ol ol 48 HR Cheistry 12 Solutios aual

6 Deterie the ass,, of C 3 H 8 (g) required, usig the olar ass ad aout i oles of propae, ad the forula =. ( ol )(44.11 g/ ol ) g 2.00 g C3H 8 Check Your Solutio The heat of cobustio of C 3 H 8 (g) is high. It is reasoable to expect a sall ass of propae to chage the teperature of water by C. The aswer has the correct uber of sigificat digits. Uit 3 Part B HR 49

7 34. A lab techicia places a 5.00 g food saple ito a bob calorieter with a heat capacity of 9.23 kj/ C. The iitial teperature of the calorieter syste is 21.0 C. After burig the food, the fial teperature of the syste is 32.0 C. How uch theral eergy is released by the cobustio of the food i kilojoules per gra? You eed to calculate the theral eergy released by the burig of a food saple. What Is Give? You kow the ass of food: food = 5.00 g You kow the heat capacity of the calorieter: C= 9.23 kj/ C You kow the iitial teperature: T iitial = 21.0ºC You kow the fial teperature: T fial = 32.0ºC Pla Your Strategy Use T = T fial T iitial to deterie the chage i teperature. Use the forula Q = C T to deterie the aout of heat, Q, gaied by the caloriter. heat give off per gra of food = Q Act o Your Strategy T Tfial Tiitial 32.0º C 21.0º C 11.0º C Q CT (9.23 kj/ C )(11 C ) kj heat give off = Q kj 5.00 g = kj/g The heat give off whe the food is bured is kj/g. Check Your Solutio The quatity of heat is a positive value sice it is absorbed by the calorieter. This is a reasoable aswer. The aswer has the correct uber of sigificat digits. 50 HR Cheistry 12 Solutios aual

8 35. Deterie the ethalpy of cobustio of a ukow fuel if a 2.75 g saple icreased the teperature of L of hot chocolate (c = 3.75 J/g C) i a g glass ug (c = 0.84 J/g C) fro C to C. Express the value for ethalpy of cobustio i appropriate uits. You eed to calculate the ethalpy of cobustio of a fuel. What Is Give? You kow the ass,, of fuel: fuel = 2.75 g You kow the volue, V, of hot chocolate: V hot chocolate = L You kow the ass,, of hot chocolate: hot chocolate = g You kow the specific heat capacity of hot chocolate: c hot chocolate = 3.75 J/g C You kow the ass of the glass ug: = g You kow the specific heat capacity of the glass ug: c glass ug You kow the iitial teperature: T iitial = 10.00ºC You kow the fial teperature: T fial = 45.00ºC ug = 0.84 J/g C Pla Your Strategy Use T = T fial T iitial to deterie the chage i teperature. Use the forula Q = c T to deterie the heat, Q, gaied by the hot chocolate ad glass ug. Assue that the desity of the hot chocolate is the sae as the desity of water. Sice E syste = E surroudigs, chage the sig of Q to fid the ethalpy chage, H, durig the cobustio. H Use the forula H cob to calculate the ethalpy of cobustio per gra of fuel. Act o Your Strategy T Tfial Tiitial 45.00º C10.00º C 35.00º C Q ( ct ) ( ct ) ug 2 chocolate [( g )(0.84 J/ g C )(35.00 C )] 2 [( g )(3.75 J/ g C 4410 J J J kj H Q kj H cob H kj 2.75 g )(35.00 C )] kj/g The ethalpy of cobustio of the fuel is 25 kj/g. Uit 3 Part B HR 51

9 Check Your Solutio The egative sig i the aswer idicates that eergy is released durig the burig of the fuel. This is reasoable. The aswer has the correct uber of sigificat digits. 52 HR Cheistry 12 Solutios aual

10 36. Urea, CO(NH 2 ) 2 (s), is widely used i various aspects of fertilizer aufacturig. A 4.28 g saple of urea is bured i a flae calorieter. The calorieter is ade of aluiu ad has a ass of 40.3 g. The L volue of water iside the calorieter is at a iitial teperature of 5.5 C. After the urea is copletely cobusted, the water teperature is 96.0 C. Use this iforatio to calculate the ethalpy of cobustio, ΔH cob, for urea. Refer to Table 5.1 for the specific heat capacity of aluiu. You eed to calculate the ethalpy of cobustio for urea. What Is Give? You kow the ass of urea: urea = 4.28 g You kow the ass of the aluiu calorieter: calorieter = 40.3 g You kow the specific heat capacity of Al(s): c Al = J/g C You kow the volue of water: V = L You kow the ass of water: =125.0 g You kow the specific heat capacity of H 2 O(l): You kow the iitial teperature: T iitial = 5.5ºC You kow the fial teperature: T fial = 96.0ºC c = 4.19 J/g C Pla Your Strategy Act o Your Strategy Deterie the aout i oles,, of CO(NH 2 ) 2 (s) cobusted, usig the ass ad olar ass of urea ad the 4.93 g forula. CH4N2O g /ol ol Use T = T fial T iitial to deterie T Tfial Tiitial the chage i teperature. 96.0º C 5.5º C 90.5º C Use the forula Q = c T to Q ( ct ) Al ( ct ) calculate the aout of heat, Q, [(40.3 g )(0.897 J/ g C )(90.5 C )] absorbed by the flae calorieter. 2 [( g )(4.19 J/ g C )(90.5 C )] J J J kj Sice E syste = E surroudigs, chage H Q the sig of Q to fid the ethalpy kj chage, H, durig the burig. Uit 3 Part B HR 53

11 o H Use the forulahcob to calculate the ethalpy of cobustio. H o cob H kj ol kj/ol The ethalpy of cobustio of urea is 617 kj/ol. Check Your Solutio The egative sig i the aswer idicates that eergy is released durig the burig of the urea. This is reasoable. The aswer has the correct uber of sigificat digits. 54 HR Cheistry 12 Solutios aual

12 37. Whe a saple of ethylee gas, C 2 H 4 (g), is bured i a ope syste, the heat produced wars 50.0 g of water by 63.0 C. The ass of C 2 H 4 (g) bured was g. a. What is the stadard olar ethalpy of cobustio for C 2 H 4 (g) i kj/ol? b. Write the therocheical equatio for this cobustio reactio. You eed to calculate the stadard olar ethalpy of cobustio for ethylee gas, C 2 H 4 (g) ad write the therocheical equatio for the cobustio reactio. What Is Give? You kow the ass of ethylee, C 2 H 4 (g): You kow the ass of water: = 50.0 g C2H4 You kow the chage i teperature: T = 63.0 C = g Pla Your Strategy Act o Your Strategy a. Deterie the aout i oles,, of C 2 H 4 (g) bured, usig the ass ad olar ass of ethylee gas ad the g C2H 4 forula g /ol ol Use the forula Q = c T to calculate Q ct the aout of heat, Q, absorbed by the (50.0 g )(4.19 J/ g C )(63 C ) water J kj Sice E syste = E surroudigs, chage H Q the sig of Q to fid the ethalpy kj chage, H, durig the burig. o H Use the forulahcob to calculate the stadard olar ethalpy of cobustio. H o cob H kj ol kj / ol b. Write the therocheical equatio for the cobustio reactio. The stadard olar ethalpy of cobustio for C 2 H 4 (g) is kj/ol. C 2 H 4 (g) + 3O 2 (g) 2CO 2 (g) + 2H 2 O(l) kj Check Your Solutio The egative sig i the aswer idicates that eergy is released durig the burig of the ethylee. This is a reasoable. The aswer has the correct uber of sigificat digits. Uit 3 Part B HR 55

13 38. Diborae, B 2 H 6 (g), is a highly reactive copoud that has bee used as a reducig aget i rocket propellats. It ca react with chlorie gas as writte below. B 2 H 6 (g) + 6Cl 2 (g) 3BCl 3 (g) + 6HCl(g) kj A 2.85 g saple of B 2 H 6 (g) reacts with a excess of chlorie gas i a bob calorieter, which is calibrated to 8.82 kj/ C. What chage i teperature will occur whe the saple reacts? You eed to fid the teperature chage whe a saple of diborae, B 2 H 6 (g), reacts. What Is Give? You kow the balaced therocheical equatio. Fro this, you kow the ethalpy of reactio, H r : 755kJ You kow the ass,, of B 2 H 6 (g): B2H6 = 2.85 g You kow the heat capacity of the calorieter: C = 8.82 kj/ C Pla Your Strategy Act o Your Strategy Deterie the aout i oles,, of B 2 H 6 (g) that reacts, usig the ass ad olar ass of diborae 2.85 g ad the forula. B2H g /ol ol Use the equatio, H = H r to calculate the ethalpy chage. Sice E syste = E surroudigs, chage the sig of H to fid the aout of heat, Q, absorbed by the calorieter ad its cotets durig the reactio. H H r ol kj QH kj kj 755 ol 56 HR Cheistry 12 Solutios aual

14 Use the forula Q = C T to deterie the chage i teperature, T. Q CT kj (8.82 kj/ C) T kj T 8.82 kj / C 8.81C The teperature is expected to icrease by 8.81 C. Check Your Solutio The egative sig i the aswer idicates that eergy is released durig the reactio of diborae ad chlorie gas. This is expected sice the teperature icreased. This is a reasoable aswer. The aswer has the correct uber of sigificat digits. Uit 3 Part B HR 57

15 39. The equatio below represets the burig of carbo disulfide, CS 2 (l), i a calorieter. What ass of CS 2 (l) ust have bured to icrease the teperature of 1.00 kg of water by 15.5 C? CS 2 (l) + 3O 2 (g) CO 2 (g) + 2SO 2 (g) kj You eed to fid the ass of carbo disulfide, CS 2 (l) that ust have bured to cause a give chage i teperature of water i a calorieter. What Is Give? You kow the balaced therocheical equatio. Fro this, you kow the ethalpy of cobustio for CS 2 (l): H cob = 1690 kj/ol You kow the ass of water: = 1.00 kg You kow the chage i teperature: T: 15.5 C Pla Your Strategy Covert the ass of water,, fro kilogras to gras. Use the equatio Q = c T to calculate the aout of heat, Q, absorbed by the water durig the burig. Sice E syste = E surroudigs, chage the sig of Q to fid the ethalpy chage, H, durig the burig kg 58 HR Cheistry 12 Solutios aual g Q ct Act o Your Strategy 3 (1 10 g/ kg 3 ( g )(4.19 J/ g C J kj H Q kj ) )(15.5 C ) H H Use the forula Hcob to Hcob deterie the aout i oles,, of kj 1690 kj/ol CS 2 (l) that bured. CS kj CS kj/ol ol Deterie the ass,, of CS 2 (l) that bured, usig the olar ass ad CS ( ol )(76.15 g/ ol ) 2 aout i oles of carbo disulfide, g ad the forula =. The ass of carbo disulfide that bured is 2.93 g. Check Your Solutio The aswer has the correct uber of sigificat digits ad sees to be a reasoable ass to produce eough theral eergy to heat 1.00 kg of water by 15.5 C.

16 40. A saple of acetoe havig a ass of g udergoes coplete cobustio i a isulated calorieter holdig L of water. It is deteried that the water ad calorieter together absorb kj of heat eergy fro this cobustio. Based upo this iforatio, what is the stadard olar ethalpy of cobustio for acetoe i kj/ol? You eed to calculate the stadard olar ethalpy of cobustio for acetoe, C 3 H 6 O(l). What Is Give? You kow the ass of acetoe: You kow the volue of water: You kow the ass of water: acetoe = g V = L = g You kow the aout of heat gaied by the water ad calorieter: Q = kj Pla Your Strategy Act o Your Strategy Deterie the aout i oles,, of C 3 H 6 O(l) cobusted, usig the ass ad olar ass of acetoe ad the g C 3H6O forula g /ol ol Sice E syste = E surroudigs, chage H Q the sig of Q to fid the ethalpy kj chage, H, durig the cobustio of the saple. o H Use the forulahcob to calculate the stadard olar ethalpy of cobustio. H o cob H kj ol 1780 kj/ol The stadard ethalpy of cobustio for acetoe is 1780 kj/ol. Check Your Solutio The egative sig i the aswer idicates that eergy is released durig the burig of the acetoe. This is a reasoable aswer. The aswer has the correct uber of sigificat digits Uit 3 Part B HR 59