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.
QUESTION 2
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Use the table below to determine ΔH for the following reaction
H 2C=CH 2(g) + F 2(g) ↔ CH 2FCH 2F(g)
Bond Energies, kJ/mol
Single Bonds
H
C
N
O
S
F
Cl
Br
I
H
432
C
411
346
N
386
305
167
O
459
358
201
142
S
363
272
---
---
286
F
565
485
283
190
284
155
Cl
428
327
313
218
255
249
240
Br
362
285
243
201
217
249
216
190
I
295
213
---
201
---
278
208
175
149
Multiple Bonds
C=C
602
C=N
615
C=O
799
C≡C
835
C≡N
887
C≡O
1072
N=N
418
N=O
607
S=O (in SO2)
532
N≡N
942
O2
494
S=O (in SO3)
469
Key Concept: ΔH° rxn = ∑ΔH ° bonds broken - ∑ΔH ° bonds formed
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