7.5 Strengths of Ionic and Covalent Bonds

Using the bond energies in the table, determine the approximate enthalpy change for each of the following reactions:

(a) $\text{H}_{2} \left(g\right) + \text{Br}_{2} \left(g\right) \rightarrow 2 \text{HBr} \left(g\right)$

(b) $\text{CH}_{4} \left(g\right) + \text{I}_{2} \left(g\right) \rightarrow \text{CH}_{3} \text{I} \left(g\right) + \text{HI} \left(g\right)$

(c) $\text{C}_{2} \text{H}_{4} \left(g\right) + 3 \text{O}_{2} \left(g\right) \rightarrow 2 \text{CO}_{2} \left(g\right) + 2 \text{H}_{2} \text{O} \left(g\right)$

Using the standard enthalpy of formation data in Appendix G, show how the standard enthalpy of formation of HCl(g) can be used to determine the bond energy.

Using the standard enthalpy of formation data in Appendix G, determine which bond is stronger: the S–F bond in SF₄(g) or in SF₆(g)?

Use principles of atomic structure to answer each of the following:This question is taken from the Chemistry Advanced Placement Examination and is used with the permission of the Educational Testing Service.

(a) The radius of the Ca atom is 197 pm; the radius of the Ca²⁺ ion is 99 pm. Account for the difference.

(b) The lattice energy of CaO(s) is –3460 kJ/mol; the lattice energy of K₂O is –2240 k…

For which of the following substances is the least energy required to convert one mole of the solid into separate ions?

(a) MgO

(b) SrO

(c) KF

(d) CsF

(e) MgF₂

The lattice energy of LiF is 1023 kJ/mol, and the Li–F distance is 201 pm. MgO crystallizes in the same structure as LiF but with a Mg–O distance of 205 pm. Which of the following values most closely approximates the lattice energy of MgO: 256 kJ/mol, 512 kJ/mol, 1023 kJ/mol, 2046 kJ/mol, or 4008 kJ/mol? Explain your choice.

Which compound in each of the following pairs has the larger lattice energy? Note: Ba²⁺ and

K⁺ have similar radii; S^2– and Cl^– have similar radii. Explain your choices.

(a) K₂O or Na₂O

(b) K₂S or BaS

(c) KCl or BaS

(d) BaS or BaCl₂

Which of the following compounds requires the most energy to convert one mole of the solid into separate ions?

(a) K₂S

(b) K₂O

(c) CaS

(d) Cs₂S

(e) CaO