Use bond energies from the table to estimate ΔrH for the following reaction. C2H2(g)+H2(g)→C2H4(g) ΔrH=? Express the answer in kJ/mol to three significant figures.
Thermochemistry
Thermochemistry can be considered as a branch of thermodynamics that deals with the connections between warmth, work, and various types of energy, formed because of different synthetic and actual cycles. Thermochemistry describes the energy changes that occur as a result of reactions or chemical changes in a substance.
Exergonic Reaction
The term exergonic is derived from the Greek word in which ‘ergon’ means work and exergonic means ‘work outside’. Exergonic reactions releases work energy. Exergonic reactions are different from exothermic reactions, the one that releases only heat energy during the course of the reaction. So, exothermic reaction is one type of exergonic reaction. Exergonic reaction releases work energy in different forms like heat, light or sound. For example, a glow stick releases light making that an exergonic reaction and not an exothermic reaction since no heat is released. Even endothermic reactions at very high temperature are exergonic.
Use bond energies from the table to estimate ΔrH for the following reaction.
C2H2(g)+H2(g)→C2H4(g) ΔrH=?
![TABLE 10.3 Some Average Bond Energiesa
Bond Energy,
kJ mol-1
Bond Energy,
kJ mol-1
Bond Energy,
kJ mol-1
Bond
Bond
Bond
H-H
436
C-C
347
N-N
163
H-C
414
C=C
C=C
611
N=N
N=N
418
H-N
389
837
946
H-0
H-S
N-O
N=0
464
C-N
305
222
368
C=N
615
590
H-F
565
C=N
891
0-0
142
H-Cl
431
360
0=0
498
Н-Br
364
736b
F-F
159
H-I
297
C-CI
339
Cl-Ci
243
Br-Br
193
I-I
151
*Although all data are listed with about the same precision (three significant figures), some
values are actually known more precisely. Specifically, the values for the diatomic mole-
cules H2, HF, HCÍ, HBr, HI, N2 (Ñ=N), O2 (0=0), F2, Cl2, Br2, and I2 are actually
bond-dissociation energies, rather than average bond energies.
ÞThe value for the C=O bonds in CO2 is 799 kJ mol-!.
You may want to reference (Page) Section 10.1 while completing this problem.](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2Fd2f6a953-4c86-4296-8437-c38226d1de8d%2Fed256a86-0fa4-49b0-a8ce-113d26b3b16c%2Fcjpkpu9_processed.png&w=3840&q=75)
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