5) C-O and O-H bonds are stronger than C-C and C-H bonds, because C-O bonds and O-H bonds S1eolar. The partial charges on the atoms result in stronger attraction between the atoms. This is why combustion reactions are exothermic and why fossil fuels are so valuable. Which of the following reactions would you predict to be endothermic? a) 200 + 4H2 → CHa + 02 b) 2H;(g) + O:(s) → 2H;O(1I) c) Na(s) + Chlg) → 2NaCi(s) d) paper burning to form CO, and H;0 6) Consider the reaction CH,OH + HBr → CH,Br + H;0 Draw the Lewis structures for reactants and products. Which bonds are broken in this reaction? Which bonds are formed? Use the table below to determine if this reaction is exothermic or endothermic and the value for AH. Table 5.4 Average Bond Enthalpies (kJ/mol) C-H 413 N-1H 391 0-H 463 155 C-C 348 N-N 163 0-0 146 614 N-O 211 C-0 495 a-F 253 C-N 293 N-1 272 0-F 190 C-a 242 C-0 358 N-a 200 0-ロ 201 C-O 799 N-ir 243 0-1 214 20 C-F 4K5 Be-a 215 C-a 328 H-H 436 一 193 C-Br 276 H-F S67 C-I 240 H-C 431 I-a H-Br 366 I-Br 175 H-1 299 1-1 151
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.
![GO and O-H bonds are stronger than C-C and C-H bonds, because C-O bonds and O-H bonds
e polar. The partial charges on the atoms result in stronger attraction between the atoms.
This is why combustion reactions are exothermic and why fossil fuels are so valuable
Which of the following reactions would you predict to be endothermic?
a) 200 + 4H2 > CHạ + 02
b) 2H2(8) + Oz(8) → 2H;O(1)
c) Na(s) + Chie) → 2NACI(s)
d) paper burning to form CO; and H20
6) Consider the reaction CH3OH + HBr > CH,Br + H;0
Draw the Lewis structures for reactants and products.
Which bonds are broken in this reaction? Which bonds are formed?
Use the table below to determine if this reaction is exothermic or endothermic and the value
for AH.
Table 5.4 Average Bond Enthalpies (kJ/mol)
C-H
413
N-H
391
0-H
463
155
C-C
348
N-N
163
0-0
146
614
N-O
201
495
d-F
253
C-N
293
N-F
272
0-F
190
C-a
242
C-O
358
N-C
200
2113
799
N-ir
24.1
0-1
234
lir-
237
C-F
485
218
C-a
328
H-H
436
Br-Br
193
C-Br
276
H-F
567
C-I
240
H-CI
431
208
H-Br
366
I-Br
175
H-I
299
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