The enthalpy change for the reaction between two molecules of carbon oxysulfide (COS) to form one molecule of CO2 and one molecule of CS2, as shown below, is –3.2 × 10–24 kJ per molecule of COS. The bond energy for the C=S bond in CS2 has been determined to be 552 kJ/mol. What is the apparent bond energy of a carbon–sulfur bond in COS? Use the bond energies below. Bonds Bond Energy (kJ/mole) C=S 552 C=O 799 Note: A C=O bond adjacent to another double bond is not the same as a C=O bond that is not adjacent to another double bond.
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.
The enthalpy change for the reaction between two molecules of carbon oxysulfide (COS) to form one molecule of CO2 and one molecule of CS2, as shown below, is –3.2 × 10–24 kJ per molecule of COS. The bond energy for the C=S bond in CS2 has been determined to be 552 kJ/mol.
What is the apparent bond energy of a carbon–sulfur bond in COS? Use the bond energies below.
| Bonds | Bond Energy (kJ/mole) |
|
C=S
|
552 |
|
C=O
|
799 |
Note: A C=O bond adjacent to another double bond is not the same as a C=O bond that is not adjacent to another double bond.
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