The isolated O 2− ion is unstable so it is not possible to measure the electron affinity of the O − ion directly. Show how you can calculate its value by using the lattice energy of MgO and the Born-Haber cycle. [Useful information: Mg( s ) → Mg( g ) Δ H ° = 148 kJ/mol.]
The isolated O 2− ion is unstable so it is not possible to measure the electron affinity of the O − ion directly. Show how you can calculate its value by using the lattice energy of MgO and the Born-Haber cycle. [Useful information: Mg( s ) → Mg( g ) Δ H ° = 148 kJ/mol.]
The isolated O2− ion is unstable so it is not possible to measure the electron affinity of the O− ion directly. Show how you can calculate its value by using the lattice energy of MgO and the Born-Haber cycle. [Useful information: Mg(s) → Mg(g) ΔH° = 148 kJ/mol.]
Definition Definition Change in energy of a neutral gaseous atom when an electron is added to the atom to form a negative ion.
Expert Solution & Answer
Interpretation Introduction
Interpretation:
Using the Born-Haber cycle for MgO lattice energy of O− has to be calculated.
Concept Introduction:
Born-Haber cycle is based on Hess’s law to calculate the lattice enthalpy of ionic compounds and deals with energy changes in formation of ionic compounds.
The energy released when gaseous state ions of unlike charges that are infinitely farther apart combine to form a stable ionic solid is called Lattice energy. Conversely, the energy required to break the electrostatic force of attraction between the ions of unlike charges in the ionic solid and revert them to gaseous state is also termed as Lattice energy of an ionic solid.
Electron affinity of an atom refers to the energy released when one electron is added to neutral atom in gaseous state.
Hess’s law is applied to calculate the enthalpy changes in a reaction. According to Hess’s law – “The overall enthalpy change of a reaction is equal to the sum of the enthalpy changes involving in each and every individual steps in the reaction.” Thus if a reaction involves ‘n’ steps then enthalpy change ΔH° of the reaction is,
ΔH°=ΔH1°+ΔH2°+ΔH3°....+ΔHn°
Answer to Problem 9.145QP
Electron affinity of O− is calculated as −844kJ/mol.
Explanation of Solution
Given data:
heat of sublimation of Mg= 148 kJ/mol
The first step of Born-Haber cycle involves sublimation of solid Mg into gaseous Mg
Mg(s)→Mg(g)ΔH1°=148kJ/mol
The second step of Born-Haber cycle involves dissociation of gaseous O2 into gaseous O atoms.
12O2(g)→O(g)ΔH2°=12(498.7)kJ/mol
The third step of Born-Haber cycle is ionization of gaseous Mg into gaseous Mg2+ ions.
The fifth and final step of Born-Haber cycle is formation of solid NaCl as a result of binding gaseous Na+ and Cl− ions together by electrostatic force of attraction.
Mg2+(g)+O(g)2−→ MgO(s)ΔH5°=−3890kJ/mol
ΔH4°'' corresponding to electron affinity of O− ion is calculated by Hess’s law as follows,
Use the Born-Haber cycle to calculate the lattice energy of KF. [The heat of sublimation of K is 91.6 kJ·mol−1 and
ΔfH(KF) = −567.3 kJ·mol−1.
Bond enthalpy for F2 is
158.8 kJ·mol−1.
Other data may be found in the Ionization Energies Table and the Electron Affinities Table.]
Using the following data, calculate the lattice energy of calcium chloride:
Ca2+(g) + 2Cl– (g) → CaCl2(s) ΔHlattice = ?
Sublimation enthalpy of calcium ΔH = 177.8 kJ/mol
First ionization energy of calcium ΔH = 590.2 kJ/mol
Second ionization energy of calcium ΔH = 1144.2 kJ/mol
First electron affinity of chlorine ΔH = –349 kJ/mol
Heat of formation of CaCl2(s) ΔH = –795.4 kJ/mol
Bond energy of Cl2 (see Table 2)
Use Hess’s law to calculate the lattice energy of calcium chloride. set-up must show all the chemical equations and you must show how their H values add up to give your answer.
Write the steps (reactions) for the Born-Haber cycle for MgCl2(s).
Use the Born-Haber cycle to calculate the lattice energy of MgCl2(s).
Some useful data to work with:
For Mg: ΔΔHsub = 147 kJ/mol, IE1 and IE2 are 738 kJ/mol and 1450 kJ/mol, respectively.
For chlorine: Bond energy = 243 kJ/mol, EA1 = -349 kJ/mol, respectively.
The enthalpy of formation of magnesium chloride is -748.8 kJ/mol.
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Author:Steven D. Gammon, Ebbing, Darrell Ebbing, Steven D., Darrell; Gammon, Darrell Ebbing; Steven D. Gammon, Darrell D.; Gammon, Ebbing; Steven D. Gammon; Darrell
Author:Steven D. Gammon, Ebbing, Darrell Ebbing, Steven D., Darrell; Gammon, Darrell Ebbing; Steven D. Gammon, Darrell D.; Gammon, Ebbing; Steven D. Gammon; Darrell