enthalpy of formation of calcium fluoride, CaF2(s), given the following data: Ca (s) → Ca (g) +179 kJ ⁄ mol Ca (g) → Ca+ (g) + e− +590 kJ ⁄ mol Ca+ (g) → Ca2+ (g) + e− +1145 kJ ⁄ mol F2 (g) → 2 F (g) +158 kJ ⁄ mol F (g) + e− → F− (g) −328 kJ ⁄ mol Ca2+ (g) + 2 F− (g) → CaF2 (s) −2630 kJ ⁄ mol A. −696 kJ ⁄ mol B. −886 kJ ⁄ mol C. −965 kJ ⁄ mol D. –1214 kJ ⁄ mol E. –1293 kJ ⁄ mol
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.
Using a Born-Haber cycle, calculate the enthalpy of formation of calcium fluoride, CaF2(s), given the
following data:
Ca (s) → Ca (g) +179 kJ ⁄ mol
Ca (g) → Ca+ (g) + e− +590 kJ ⁄ mol
Ca+ (g) → Ca2+ (g) + e− +1145 kJ ⁄ mol
F2 (g) → 2 F (g) +158 kJ ⁄ mol
F (g) + e− → F− (g) −328 kJ ⁄ mol
Ca2+ (g) + 2 F− (g) → CaF2 (s) −2630 kJ ⁄ mol
A. −696 kJ ⁄ mol
B. −886 kJ ⁄ mol
C. −965 kJ ⁄ mol
D. –1214 kJ ⁄ mol
E. –1293 kJ ⁄ mol
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