Calculate the enthalpies of formation, Δ?∘f,ΔHf∘, of group 1 chloride compounds from their elements by using the Born–Haber cycle. Process Δ?∘, kJ/molΔH∘, kJ/mol Sublimation of K(s)K(s) 90 Sublimation of Rb(s)Rb(s) 86 Dissociation of Cl2(g)Cl2(g) 244 Ionization energy of K(g)K(g) 419 Ionization energy of Rb(g)Rb(g) 403 Electron affinity of Cl(g)Cl(g) −349 Lattice enthalpy of KCl(s)KCl(s) 717 Lattice enthalpy of RbCl(s)RbCl(s) 695 Δ?∘fΔHf∘ of KCl=KCl=
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 the enthalpies of formation, Δ?∘f,ΔHf∘, of group 1 chloride compounds from their elements by using the Born–Haber cycle.
| Process | Δ?∘, kJ/molΔH∘, kJ/mol |
|---|---|
| Sublimation of K(s)K(s) | 90 |
| Sublimation of Rb(s)Rb(s) | 86 |
| Dissociation of Cl2(g)Cl2(g) | 244 |
| Ionization energy of K(g)K(g) | 419 |
| Ionization energy of Rb(g)Rb(g) | 403 |
| −349 | |
| Lattice enthalpy of KCl(s)KCl(s) | 717 |
| Lattice enthalpy of RbCl(s)RbCl(s) | 695 |
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