Lattice energy cannot be determined experimentally due to the difficulty in isolating gaseous ions. The energy value can be estimated using the Born-Haber cycle, or it can be calculated theoretically with an electrostatic examination of the crystal structure. This model emphasizes two main factors that contribute to the lattice energy of an ionic solid: the charge on the ions, and the radius, or size, of the ions. The effect of those factors is:. Lattice energies are also important in predicting the solubility of ionic solids in H 2 O.
Reaction 1. This equation describes the sublimation The conversion of a solid directly to a gas without an intervening liquid phase. Reaction 2. This equation describes the ionization of cesium, so the enthalpy change is the first ionization energy of cesium. Hence, regardless of the compound, the enthalpy change for this portion of the Born—Haber cycle is always positive. Reaction 3. This equation describes the dissociation of fluorine molecules into fluorine atoms, where D is the energy required for dissociation to occur Table 8.
We need to dissociate only 1 2 mol of F 2 g molecules to obtain 1 mol of F g atoms. Reaction 4. This equation describes the formation of a gaseous fluoride ion from a fluorine atom; the enthalpy change is the electron affinity of fluorine. Recall from Chapter 7 "The Periodic Table and Periodic Trends" that electron affinities can be positive, negative, or zero. Reaction 5. This equation describes the formation of the ionic solid from the gaseous ions.
We can rearrange Equation 8. Substituting the appropriate values into this equation gives. U is larger in magnitude than any of the other quantities in Equation 8. The process we have used to arrive at this value is summarized in Table 8.
Equation 8. Thus the first three terms in Equation 8. This means that lattice energy is the most important factor in determining the stability of an ionic compound. Another example is the formation of BaO:.
The lattice energy of BaO, with a dipositive cation and a dinegative anion, dominates the Born—Haber cycle. More than twice as much energy is required to sublime barium metal Because the bond energy of O 2 g is The answer is the formation of the ionic solid from the gaseous ions Reaction 5 :. Remember from Equation 8.
Although the internuclear distances are not significantly different for BaO and CsF and pm, respectively , the larger ionic charges in BaO produce a much higher lattice energy. Lattice energy is usually the most important energy factor in determining the stability of an ionic compound. Use data from Figure 7. Given: chemical compound and data from figures and tables. Asked for: lattice energy. A Write a series of stepwise reactions for forming MgH 2 from its elements via the gaseous ions.
We begin by writing reactions in which we form the component ions from the elements in a stepwise manner and then assemble the ionic solid:. B Table 7. Use the data given below to construct a Born-Haber cycle to determine th The formation of CsCl from Cs s and Cl2 g involves the following steps Watch concept videos about Born Haber Cycle.
Question The lattice energy of potassium iodide is the energy required for the following reaction. Submit Comment. Sign up to view answer. Sign up for free to see the solution Continue with Gmail Continue with Facebook or continue watching with email "Clutch really helped me by reinforcing the things I learned in class and making exam reviews a breeze. The ionic bond should also become stronger as the charge on the ions becomes larger.
The data in the table below show that the lattice energies for salts of the OH - and O 2- ions increase rapidly as the charge on the ion becomes larger. When a salt, such as NaCl dissolves in water, the crystals disappear on the macroscopic scale.
0コメント