I. AHxn for the reaction below was determined using bond dissociation energies (BDES) to be -57 kJ. Using the table of BDE below, find the bond energy for H-Br. H C=C H H Br Н-С-ҫ-н + HBr H Bond С-С C=C C-H C-Br BDE (kJ/mol) 348 614 413 276 II. Use heats of formation to find the standard heat of reaction (AH° xn) for the reaction shown above. C2H4 and HBr are both gases and AH°; for CH3CH,Br (8) is -85.3 kJ/mol. Use T16-4-1 to find any additional values of AH°; needed. III. Why is there a dfference between the reaction enthalpies calculated by these different approaches?

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I. AHn for the reaction below was determined using bond dissociation energies (BDES) to be -57 kJ. Using the table of BDE below,
find the bond energy for H-Br.
'rxn
H Br
H
c=C
H
+ HBr
+ H-C-C-
H
Bond
С-С
C=C
C-H
С-Br
BDE (kJ/mol)
348
614
413
276
II. Use heats of formation to find the standard heat of reaction (AH° rxn) for the reaction shown above. C2H4 and HBr are both gases and
AH°; for CH3CH2B (8) is -85.3 kJ/mol. Use T16-4-1 to find any additional values of AH°; needed.
III. Why is there a dfference between the reaction enthalpies calculated by these different approaches?
Transcribed Image Text:I. AHn for the reaction below was determined using bond dissociation energies (BDES) to be -57 kJ. Using the table of BDE below, find the bond energy for H-Br. 'rxn H Br H c=C H + HBr + H-C-C- H Bond С-С C=C C-H С-Br BDE (kJ/mol) 348 614 413 276 II. Use heats of formation to find the standard heat of reaction (AH° rxn) for the reaction shown above. C2H4 and HBr are both gases and AH°; for CH3CH2B (8) is -85.3 kJ/mol. Use T16-4-1 to find any additional values of AH°; needed. III. Why is there a dfference between the reaction enthalpies calculated by these different approaches?
The standard enthalpies of formation are available for a large number of compounds
in thermodynamic tables
Table T16-4-1. Selected standard enthalpies of formation, AH°;(298 K, 1 atm)
AH°f
AH°f
Substance
Formula
Substance
Formula
(kJ/mol)
(kJ/mol)
acetic acid
C2H4O2(!)
-487.0 hydrogen bromide
HBr(g)
-36.2
- .......
acetylene
C2H2(g)
226.8 hydrogen chloride
HCI(g)
-92.3
ammonia
NH 3(g)
-46.2 hydrogen fluoride
HF(g)
-268.6
aluminum oxide
Al 203(s)
-1675.7 hydrogen iodide
HI(g)
25.9
-.................
benzene
C6H6(t)
49.0 hydrogen peroxide
H202({)
-187.8
bromine
Br 2(g)
30.907 iron(II) oxide
Fe203(s)
-824.2
calcium carbonate
CaCO 3(s)
-1207.1 methane
CH 4(g)
-74.8
calcium oxide
CaO(s)
-635.5 methanol
CH3OH(t)
-238.6
carbon dioxide
CO 2(g)
-393.5
O 3(g)
142.3
Ozone
carbon monoxide
CO(g)
-110.5 propane
C3H8(g)
-103.8
carbon tetrachloride
CCI 4(!)
-193.3 silver chloride
AgCI( s)
-127.0
diamond
C(s)
1.9 sodium bicarbonate
NaHCO 3(s)
-947.7
ethane
C2H6(g)
-84.7 sodium carbonate
Na 2CO3(s)
-1130.9
ethanol
C2H5OH(g)
-235.1 sodium chloride
NaCI(s)
-410.9
ethanol
C2H5OH(?)
-277.7 sodium hydroxide
NaOH(s)
-425.6
ethyl bromide
C2H3Br(g)
-97.6
sucrose
C 12H22011(s)
-2221.0
ethylene
C2H4(g)
52.3 sulfur trioxide
SO 3(g)
-395.2
formaldehyde
CH20(g)
-108.6 water
H20(t)
-285.8
glucose
C6H1206(s)
-1273.0 water vapor
H20(g)
-241.8
Transcribed Image Text:The standard enthalpies of formation are available for a large number of compounds in thermodynamic tables Table T16-4-1. Selected standard enthalpies of formation, AH°;(298 K, 1 atm) AH°f AH°f Substance Formula Substance Formula (kJ/mol) (kJ/mol) acetic acid C2H4O2(!) -487.0 hydrogen bromide HBr(g) -36.2 - ....... acetylene C2H2(g) 226.8 hydrogen chloride HCI(g) -92.3 ammonia NH 3(g) -46.2 hydrogen fluoride HF(g) -268.6 aluminum oxide Al 203(s) -1675.7 hydrogen iodide HI(g) 25.9 -................. benzene C6H6(t) 49.0 hydrogen peroxide H202({) -187.8 bromine Br 2(g) 30.907 iron(II) oxide Fe203(s) -824.2 calcium carbonate CaCO 3(s) -1207.1 methane CH 4(g) -74.8 calcium oxide CaO(s) -635.5 methanol CH3OH(t) -238.6 carbon dioxide CO 2(g) -393.5 O 3(g) 142.3 Ozone carbon monoxide CO(g) -110.5 propane C3H8(g) -103.8 carbon tetrachloride CCI 4(!) -193.3 silver chloride AgCI( s) -127.0 diamond C(s) 1.9 sodium bicarbonate NaHCO 3(s) -947.7 ethane C2H6(g) -84.7 sodium carbonate Na 2CO3(s) -1130.9 ethanol C2H5OH(g) -235.1 sodium chloride NaCI(s) -410.9 ethanol C2H5OH(?) -277.7 sodium hydroxide NaOH(s) -425.6 ethyl bromide C2H3Br(g) -97.6 sucrose C 12H22011(s) -2221.0 ethylene C2H4(g) 52.3 sulfur trioxide SO 3(g) -395.2 formaldehyde CH20(g) -108.6 water H20(t) -285.8 glucose C6H1206(s) -1273.0 water vapor H20(g) -241.8
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