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Ch.8 - Basic Concepts of Chemical Bonding
Brown - Chemistry: The Central Science 15th Edition
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Tutti i libri di testoBrown 15th EditionCh.8 - Basic Concepts of Chemical BondingProblema 31
Capitolo 8, Problema 31

Use data from Appendix C, Figure 7.11, and Figure 7.13 to calculate the lattice energy of KI.

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Identify the Born-Haber cycle for KI, which involves the following steps: sublimation of K(s) to K(g), ionization of K(g) to K^+(g), dissociation of I2(g) to 2 I(g), electron affinity of I(g) to I^-(g), and formation of KI(s) from K^+(g) and I^-(g).
Use Appendix C to find the enthalpy of sublimation for K(s) to K(g).
Use Appendix C to find the ionization energy for K(g) to K^+(g).
Use Appendix C to find the bond dissociation energy for I2(g) to 2 I(g), and then calculate the energy for I(g) to I^-(g) using the electron affinity.
Apply Hess's Law to sum the enthalpies of each step in the Born-Haber cycle, including the lattice energy, to solve for the lattice energy of KI.

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Lattice Energy

Lattice energy is the amount of energy released when gaseous ions combine to form an ionic solid. It is a measure of the strength of the forces between the ions in an ionic compound. Higher lattice energy indicates stronger ionic bonds, which typically results in higher melting points and greater stability of the compound.
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Lattice Energy

Born-Haber Cycle

The Born-Haber cycle is a thermodynamic cycle that relates the lattice energy of an ionic compound to other energy changes involved in its formation. It includes steps such as ionization energy, electron affinity, and sublimation energy, allowing for the calculation of lattice energy using Hess's law. This cycle is essential for understanding how different energy contributions affect the overall stability of ionic compounds.
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Born Haber Cycle

Ionic Radii

Ionic radii refer to the effective size of an ion in a crystal lattice. The size of the ions affects the distance between them, which in turn influences the lattice energy. Smaller ions can pack more closely together, leading to stronger electrostatic attractions and higher lattice energies, while larger ions result in weaker attractions and lower lattice energies.
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Ranking Ionic Radii
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Domanda del libro di testo

Energy is required to remove two electrons from Ca to form Ca2+, and energy is required to add two electrons to O to form O2 - . Yet CaO is stable relative to the free elements. Which statement is the best explanation? (a) The lattice energy of CaO is large enough to overcome these processes. (b) CaO is a covalent compound, and these processes are irrelevant. (c) CaO has a higher molar mass than either Ca or O. (d) The enthalpy of formation of CaO is small. (e) CaO is stable to atmospheric conditions.

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Domanda del libro di testo

List the individual steps used in constructing a Born–Haber cycle for the formation of BaI2 from the elements. Which of the steps would you expect to be exothermic?

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Domanda del libro di testo

Which of the following trends in lattice energy is due to differences in ionic radii: a. NaCl > RbBr > CsBr, b. BaO > KF, c. SrO > SrCl2?


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Domanda del libro di testo

(a) Based on the lattice energies of MgCl2 and SrCl2 given in Table 8.1, what is the range of values that you would expect for the lattice energy of CaCl2?

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(b) Using data from Appendix C, Figure 7.11, Figure 7.13, and the value of the second ionization energy for Ca, 1145 kJ/mol, calculate the lattice energy of CaCl2.

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Domanda del libro di testo

(b) A substance, XY, formed from two different elements, melts at −33 °C. Is XY likely to be a covalent or an ionic substance?

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