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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 30
Capitolo 8, Problema 30

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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Write the overall reaction for the formation of BaI_2 from its elements: Ba(s) + I_2(s) -> BaI_2(s).
Sublimation of solid barium to gaseous barium: Ba(s) -> Ba(g). This step requires energy input, so it is endothermic.
Ionization of gaseous barium to form Ba^2+: Ba(g) -> Ba^2+(g) + 2e^-. This step is endothermic as it requires energy to remove electrons.
Dissociation of iodine molecules into iodine atoms: I_2(s) -> 2I(g). This step is endothermic because energy is needed to break the I-I bond.
Formation of iodide ions from iodine atoms: I(g) + e^- -> I^-(g). This step is exothermic as energy is released when an electron is added to an iodine atom.

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Born-Haber Cycle

The Born-Haber cycle is a thermodynamic cycle that relates the lattice energy of an ionic compound to the enthalpy changes involved in its formation from the constituent elements. It provides a systematic way to calculate the lattice energy by considering the various steps, including sublimation, ionization, and electron affinity, that occur when forming an ionic compound from its elements.
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Born Haber Cycle

Lattice Energy

Lattice energy is the energy released when gaseous ions combine to form an ionic solid. It is a crucial factor in determining the stability of ionic compounds. In the context of the Born-Haber cycle, lattice energy is typically a large exothermic value, indicating that the formation of the ionic lattice from gaseous ions is energetically favorable.
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Lattice Energy

Enthalpy Changes

Enthalpy changes refer to the heat absorbed or released during a chemical reaction at constant pressure. In the Born-Haber cycle, various steps involve enthalpy changes, such as the enthalpy of sublimation, ionization energy, and electron affinity. Understanding which steps are exothermic (release heat) or endothermic (absorb heat) is essential for predicting the overall energy change in the formation of the compound.
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Enthalpy of Formation
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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

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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Consider the ionic compounds KF, NaCl, NaBr, and LiCl. (a) Use ionic radii (Figure 7.8) to estimate the cation–anion distance for each compound.

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

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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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