The lattice energy of potassium iodide is the energy required for the following reaction. KI(s) → K+(g) + I−(g) ΔHrxn = ΔHlattice Use the Born-Haber cycle to calculate ΔHlattice for KI(s) from the information given below. Equation 1: 2 K(s) + I2(g) → 2 KI(s) ΔH1 = −655 kJ/mol Equation 2: K(s) → K(g) ΔH2 = 89 kJ/mol Equation 3: I2(g) → 2 I(g) ΔH3 = 214 kJ/mol Equation 4: K(g) → K+(g) + e− ΔH4 = 419 kJ/mol Equation 5: I(g) + e− → I−(g) ΔH5 = −294 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.
The lattice energy of potassium iodide is the energy required for the following reaction. KI(s) → K+(g) + I−(g) ΔHrxn = ΔHlattice
Use the Born-Haber cycle to calculate ΔHlattice for KI(s) from the information given below.
| Equation 1: 2 K(s) + I2(g) → 2 KI(s) | ΔH1 = −655 kJ/mol | |
| Equation 2: K(s) → K(g) | ΔH2 = 89 kJ/mol | |
| Equation 3: I2(g) → 2 I(g) | ΔH3 = 214 kJ/mol | |
| Equation 4: K(g) → K+(g) + e− | ΔH4 = 419 kJ/mol | |
| Equation 5: I(g) + e− → I−(g) | ΔH5 = −294 kJ/mol |
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