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Chapter 8: Problem 55

Which compound in each of the following pairs of ionic substances has the most exothermic lattice energy? Justify your answers. a. \(\mathrm{NaCl}, \mathrm{KCl}\) b. \(\mathrm{LiF}, \mathrm{LiCl}\) c. \(\mathrm{Mg}(\mathrm{OH})_{2}, \mathrm{MgO}\) d. \(\mathrm{Fe}(\mathrm{OH})_{2}, \mathrm{Fe}(\mathrm{OH})_{3}\) e. \(\mathrm{NaCl}, \mathrm{Na}_{2} \mathrm{O}\) f. \(\mathrm{MgO}\), BaS

Short Answer

Expert verified
In summary, the compounds with the most exothermic lattice energy in each pair are: a. \(\mathrm{NaCl}\) b. \(\mathrm{LiF}\) c. \(\mathrm{MgO}\) d. \(\mathrm{Fe}(\mathrm{OH})_{3}\) e. \(\mathrm{Na}_{2} \mathrm{O}\) f. \(\mathrm{MgO}\) The lattice energy depends on the ionic charges and ion sizes, with higher charges and smaller ion sizes resulting in more exothermic lattice energies.

Step by step solution

01

Compare \(\mathrm{NaCl}\) and \(\mathrm{KCl}\)

Recall that the ionic charge of Na is +1 and that of Cl is -1. The same holds for K and Cl. However, K has a larger atomic radius than Na. So, in this case, \(\mathrm{NaCl}\) will have a more exothermic lattice energy, as smaller ions result in greater lattice energy.
02

Compare \(\mathrm{LiF}\) and \(\mathrm{LiCl}\)

In this case, Li has a charge of +1, while F has a charge of -1, and Cl has a charge of -1 as well. F has a smaller atomic radius than Cl. So, \(\mathrm{LiF}\) will have a more exothermic lattice energy due to its smaller ion size.
03

Compare \(\mathrm{Mg}(\mathrm{OH})_{2}\) and \(\mathrm{MgO}\)

Mg has a charge of +2, O has a charge of -2, and OH has a charge of -1. Since MgO has higher ionic charges than Mg(OH)\(_{2}\), it will have a more exothermic lattice energy.
04

Compare \(\mathrm{Fe}(\mathrm{OH})_{2}\) and \(\mathrm{Fe}(\mathrm{OH})_{3}\)

Fe has a charge of +2 in \(\mathrm{Fe}(\mathrm{OH})_{2}\) and +3 in \(\mathrm{Fe}(\mathrm{OH})_{3}\). OH has a charge of -1. Due to the higher charge in \(\mathrm{Fe}(\mathrm{OH})_{3}\), it will have a more exothermic lattice energy.
05

Compare \(\mathrm{NaCl}\) and \(\mathrm{Na}_2\mathrm{O}\)

Na has a charge of +1, Cl has a charge of -1, and O has a charge of -2. The ionic charges are greater in \(\mathrm{Na}_{2}\mathrm{O}\) than in \(\mathrm{NaCl}\), resulting in a more exothermic lattice energy for \(\mathrm{Na}_{2}\mathrm{O}\).
06

Compare \(\mathrm{MgO}\) and \(\mathrm{BaS}\)

Mg has a charge of +2, O has a charge of -2, Ba has a charge of +2, and S has a charge of -2. Though the ionic charges are the same in both compounds, Mg has a smaller atomic radius than Ba. As a result, \(\mathrm{MgO}\) will have a more exothermic lattice energy due to its smaller ion size.

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Most popular questions from this chapter

Arrange the atoms and/or ions in the following groups in order of decreasing size. a. \(\mathrm{O}, \mathrm{O}^{-}, \mathrm{O}^{2-}\) b. \(\mathrm{Fe}^{2+}, \mathrm{Ni}^{2+}, \mathrm{Zn}^{2+}\) c. \(\mathrm{Ca}^{2+}, \mathrm{K}^{+}, \mathrm{Cl}^{-}\)

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