Part A Consider the hypothetical reaction between two diatomic molecules in the gas phase: X-X(g)+Y–Y(g)→ 2X–Y(g) Based on the bond enthalpies in the table shown, how many of the following combinations of X and Y are predicted to lead to exothermic reactions? (i) X = H, Y = F; (ii) X = H, Y = Br; (ii)X = F, Y = Cl; (iv) X = CI, Y = 1.
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.
![Average Bond Enthalpies (kJ/mol)
Part A
C-H 413 N-H 391 0-H 463 F-F 155
C-C 348 N-N
C=C 614 N-O 201 O=0
163 0-0 146
Consider the hypothetical reaction between two diatomic molecules in the gas phase:
495 Cl-F 253
C-N 293 N-F 272 0-F 190 Cl-CI 242
X-X(g)+ Y-Y(g)→ 2X-Y(g)
C-0 358 N-Cl 200 0-Cl 203 Br-F 237
C=0 799 N-Br 243 0-I
Based on the bond enthalpies in the table shown, how many of the following combinations of X and Y are
predicted to lead to exothermic reactions? (i) X = H, Y = F; (ii) X = H, Y = Br; (iii) X = F, Y = Cl; (iv) X = CI,
Y = .
234 Br-Cl 218
С -F 485 | Н-Н 436
C-Cl 328 H–F
Br-Br 193
567
C-Br 276 H-CI 431
I-C 208
240 H-Br 366
H-I 299
C-I
I-Br 175
O 1
I-I
151
O 2
combinations will lead to an exothermic reaction.
O 3
O 4](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2F108a0acc-c86a-4fb9-81b6-4d3403f04067%2F2d0cbda0-902a-4678-b5b4-9e9e876de1fa%2Fgwn9kvf_processed.png&w=3840&q=75)
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