formula but different arrangements of atoms. Use Table 8.3to estimate AH for each of the following gas-phase isomer-ization reactions and indicate which isomer has the lowerenthalpyH HI I(а) Н—С—С—0-н — Н-С-0-С-ННнEthanolDimethyl etherно— Н—С—С—Н(b) Н——С-HT IнннAcetaldehydeEthylene oxideН,Н.нH HHHH I|С—С—С—С-С—Н(c) HНHн'PentadieneCyclopenteneННН-С—NEC — Н—С-СEN(d)ННMethyl isocyanideAcetonitrile | Strengths and Lengths8.8of Covalent BondsThe stability of a molecule is related to the strengths of its covalent bonds. We saw in Chapter 5that we can measure the average bond enthalpy of many single bonds (Table 5.4). Table 5.4 isrepeated here as Table 8.3. As you might expect, Table 8.3 shows that multiple bonds aregenerally stronger than single bondsTABLE 8.3 Average Bond Enthalpies (k)J/mol)Single Bonds413N-H391о--нF-F463155С-нN-N163348О-О146С-сN-O201293О-F190Cl-F253C-NN-FО— СI272358203Cl-Cl242С-оN-CI200О-1485234С-FN-Br243328Br-F237C-CI276S-H339Br-Cl218С-BrН--Н436SF240327Br-Br193С-1Н-F567S-Cl259253С-SН-СI431S-Br218I-CI208Н- Br366323S-S266I--BrSi-H175Н-I299226Si-SiI-I151301Si-C368Si-O464Si-ClMultiple BondsC=C614N=N418O=O495C=C839N=N941C=N615N- O607S=O523C=N891S=S418C=O799C O1072

Question
Asked Oct 16, 2019
formula but different arrangements of atoms. Use Table 8.3
to estimate AH for each of the following gas-phase isomer-
ization reactions and indicate which isomer has the lower
enthalpy
H H
I I
(а) Н—С—С—0-н — Н-С-0-С-Н
Нн
Ethanol
Dimethyl ether
но
— Н—С—С—Н
(b) Н——С-H
T I
нн
н
Acetaldehyde
Ethylene oxide
Н,
Н.
н
H HHH
H I|
С—С—С—С-С—Н
(c) H
Н
H
н'
Pentadiene
Cyclopentene
Н
Н
Н-С—NEC — Н—С-СEN
(d)
Н
Н
Methyl isocyanide
Acetonitrile
help_outline

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formula but different arrangements of atoms. Use Table 8.3 to estimate AH for each of the following gas-phase isomer- ization reactions and indicate which isomer has the lower enthalpy H H I I (а) Н—С—С—0-н — Н-С-0-С-Н Нн Ethanol Dimethyl ether но — Н—С—С—Н (b) Н——С-H T I нн н Acetaldehyde Ethylene oxide Н, Н. н H HHH H I| С—С—С—С-С—Н (c) H Н H н' Pentadiene Cyclopentene Н Н Н-С—NEC — Н—С-СEN (d) Н Н Methyl isocyanide Acetonitrile

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| Strengths and Lengths
8.8
of Covalent Bonds
The stability of a molecule is related to the strengths of its covalent bonds. We saw in Chapter 5
that we can measure the average bond enthalpy of many single bonds (Table 5.4). Table 5.4 is
repeated here as Table 8.3. As you might expect, Table 8.3 shows that multiple bonds are
generally stronger than single bonds
TABLE 8.3 Average Bond Enthalpies (k)J/mol)
Single Bonds
413
N-H
391
о--н
F-F
463
155
С-н
N-N
163
348
О-О
146
С-с
N-O
201
293
О-F
190
Cl-F
253
C-N
N-F
О— СI
272
358
203
Cl-Cl
242
С-о
N-CI
200
О-1
485
234
С-F
N-Br
243
328
Br-F
237
C-CI
276
S-H
339
Br-Cl
218
С-Br
Н--Н
436
SF
240
327
Br-Br
193
С-1
Н-F
567
S-Cl
259
253
С-S
Н-СI
431
S-Br
218
I-CI
208
Н- Br
366
323
S-S
266
I--Br
Si-H
175
Н-I
299
226
Si-Si
I-I
151
301
Si-C
368
Si-O
464
Si-Cl
Multiple Bonds
C=C
614
N=N
418
O=O
495
C=C
839
N=N
941
C=N
615
N- O
607
S=O
523
C=N
891
S=S
418
C=O
799
C O
1072
help_outline

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| Strengths and Lengths 8.8 of Covalent Bonds The stability of a molecule is related to the strengths of its covalent bonds. We saw in Chapter 5 that we can measure the average bond enthalpy of many single bonds (Table 5.4). Table 5.4 is repeated here as Table 8.3. As you might expect, Table 8.3 shows that multiple bonds are generally stronger than single bonds TABLE 8.3 Average Bond Enthalpies (k)J/mol) Single Bonds 413 N-H 391 о--н F-F 463 155 С-н N-N 163 348 О-О 146 С-с N-O 201 293 О-F 190 Cl-F 253 C-N N-F О— СI 272 358 203 Cl-Cl 242 С-о N-CI 200 О-1 485 234 С-F N-Br 243 328 Br-F 237 C-CI 276 S-H 339 Br-Cl 218 С-Br Н--Н 436 SF 240 327 Br-Br 193 С-1 Н-F 567 S-Cl 259 253 С-S Н-СI 431 S-Br 218 I-CI 208 Н- Br 366 323 S-S 266 I--Br Si-H 175 Н-I 299 226 Si-Si I-I 151 301 Si-C 368 Si-O 464 Si-Cl Multiple Bonds C=C 614 N=N 418 O=O 495 C=C 839 N=N 941 C=N 615 N- O 607 S=O 523 C=N 891 S=S 418 C=O 799 C O 1072

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check_circleExpert Solution
Step 1

(a)The enthalpy of ethanol to dimethyl ether isomerization reaction is 

BE (reactants)=sum of bond broken enthalpies of rea ctants
BE (products)sumof bond formedenthalpies of products
BE (ethanol) 347kJ/mol+358 kJ/mol+467 kJ/mol-1172KJ/mol
BE(dimethyl e ther) =413 kJ/mol +358 kJ/mol+358 kJ/mol =1129 kJ/mol
ΔΗ-ΣΒΕ (reactants) -ΣΒΕ (produ cts)
-1172 kJ/mol -1129 kJ/mol
43KJ/mol
Isomer with lower enthalpyis Ethanol
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BE (reactants)=sum of bond broken enthalpies of rea ctants BE (products)sumof bond formedenthalpies of products BE (ethanol) 347kJ/mol+358 kJ/mol+467 kJ/mol-1172KJ/mol BE(dimethyl e ther) =413 kJ/mol +358 kJ/mol+358 kJ/mol =1129 kJ/mol ΔΗ-ΣΒΕ (reactants) -ΣΒΕ (produ cts) -1172 kJ/mol -1129 kJ/mol 43KJ/mol Isomer with lower enthalpyis Ethanol

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Step 2

(b)The enthalpy of ethylene oxide to acetaldehyde isomerization reaction is 

BE (ethylene oxide) 358KJ/mol +35 8 kJ/mol = 716 kJ/mol
BE (acetaldehyde)-745 kJ/mol-745KJ/mol
AH-BE (reactants)-BE (products)
716kJ/mol-745KJ/mol
=-29KJ/mol
Isomer with lowerenthalpyis A cetaldehyde
help_outline

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BE (ethylene oxide) 358KJ/mol +35 8 kJ/mol = 716 kJ/mol BE (acetaldehyde)-745 kJ/mol-745KJ/mol AH-BE (reactants)-BE (products) 716kJ/mol-745KJ/mol =-29KJ/mol Isomer with lowerenthalpyis A cetaldehyde

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Step 3

(c)The enthalpy of cyclopentene to pentadi...

BE(cyclopentene)=347kJ/mol+347 kJ/mol=694 kJ/mol
BE (pentadiene)=614 kJ/mol= 614 kJ/mol
AH-BE (reactants)-BE (products)
-694kJ/mol-614kJ/mol
=80KJ/mol
Isomer with lower enthalpy is Cyclopentene
help_outline

Image Transcriptionclose

BE(cyclopentene)=347kJ/mol+347 kJ/mol=694 kJ/mol BE (pentadiene)=614 kJ/mol= 614 kJ/mol AH-BE (reactants)-BE (products) -694kJ/mol-614kJ/mol =80KJ/mol Isomer with lower enthalpy is Cyclopentene

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