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.
![Calculate AG for the formation of one mole of
N₂O4 from its elements using AH and ASfº for
N₂O4.
Use data in the table below:
Substance
Ag(s)
AgCl(s)
Al(s)
Al₂O3(s)
C(s) (graphite)
(8)
CO₂(g)
CH₂(g)
CH₂Cl(g)
CH₂OH(1)
C₂H₂(g)
C₂H4(g)
C₂H6(g)
C8H18 (7)
C₂H₂OH(1)
Ca(s)
CaCO3(s)
CaCl₂(s)
197.9
213.6
186.2
234.2
126.8
CO(NH,),(s) 104.6
CO(NH,),(aq) 173.8
200.8
219.8
229.5
466.9
161
CO(g)
CO₂(g)
CH4(g)
Substance
Ag(s)
AgBr(s)
AgCl(s)
Al(s)
Al₂O3(s)
C(s) (graphite)
Standard Entropies of Some Typical Substances at 298.15 K
Sº
(J mol-¹ K-¹)
40
76.1
107
C₂H₂(g)
C₂H4(g)
C₂H6(g)
C₂H,OH(1)
Ca(s)
CaBr₂(s)
CaCO3(s)
CaCl₂(s)
CaO(s)
Cl₂(g)
Fe(s)
Sᵒ
(J mol-¹ K-¹)
Fe₂O3(s)
H₂(g)
H₂O(g)
H₂O(1)
AGO =
CH₂Cl(g)
CH₂I(g)
CH₂OH(1)
CO(NH₂)2(s) (urea)
CO(NH,),(aq)
kJ mol-1
42.55
96.2
28.3
51.0
Ca(OH)₂(s)
CaSO4(s)
CaSO4 H₂O(s)
CaSO4-2H₂O(s)
5.69
41.4
92.9
114
Substance
CaO(s)
Ca(OH)₂(s)
CaSO4(s)
CaSO4+H₂O(s) 131
CaSO4-2H₂O(s) 194.0
223.0
27
Cl₂(g)
Fe(s)
Fe₂O3(s)
H₂(g)
H₂O(g)
H₂O(1)
HCI(g)
HNO3(1)
H₂SO4(1)
HC,H,O,(0)
Hg(1)
Hg(g)
K(s)
KCI(s)
K₂SO4(s)
-74.848
-82.0
14.2
-238.6
-333.19
-391.2
226.75
52.284
-84.667
-277.63
0
-682.8
-1207
Standard Enthalpies of Formation of Typical Substances
AH; (kJ mol-¹)
Substance
0
- 100.4
- 127.0
0
- 1669.8
0
-110.5
-393.5
-795.0
-635.5
-986.59
90.0
130.6
188.7
-1432.7
-1575.2
-2021.1
0
0
-822.2
0
-241.8
-285.9
69.96
186.7
155.6
157
160
76.1
175
64.18
82.59
176
H₂O₂(1)
HBr(g)
HCI(g)
HI(g)
HNO3(1)
H₂SO4(1)
HC,H,O,(0)
Hg(1)
Hg(g)
1₂ (s)
K(s)
KCI(s)
K₂SO4(s)
N₂(g)
NH3(g)
NH₂Cl(s)
NO(g)
NO₂(g)
N₂O(g)
N₂O4(g)
N₂O5(g)
Na(s)
NaHCO3(s)
Na₂CO3(s)
NaCl(s)
NaOH(s)
Na₂SO4(s)
0₂(8)
Pb(s)
Substance
N₂(g)
NH3(g)
NH₂Cl(s)
NO(g)
NO₂(g)
N₂O(g)
N₂O4(g)
Na(s)
PbO(s)
S(s)
SO₂(g)
SO3(g)
Na₂CO3(s)
NaHCO3(s)
NaCl(s)
NaOH(s)
Na₂SO4(s)
O₂(g)
PbO(s)
S(s)
SO₂(g)
SO3(g)
Sº
(J mol-¹ K-¹)
191.5
192.5
94.6
210.6
240.5
220.0
304
AH; (kJ mol-¹)
-187.6
-36
-1433.7
0
-46.19
-92.30
26.6
- 173.2
-811.32
-487.0
0
60.84
0
0
-435.89
-315.4
90.37
33.8
81.57
9.67
11
0
-947.7
-1131
136
102
-411.0
-426.8
- 1384.5
0
0
-219.2
0
-296.9
-395.2
51.0
149.4
205.0
67.8
31.9
248.5
256.2
72.38
64.18](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2F80adb728-6954-4f8d-9107-41647af52006%2Fa0959351-fd9d-4f5f-92d6-1e7ace8d4923%2Ffg28hi8_processed.jpeg&w=3840&q=75)
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