Chapter 3, Problem 24P

Use the data in Figure 3.11 and Table 3.2 to calculate the energy changes $\left(\Delta \text{E}\right)$ for the following pairs of reactions:

(a) $\text{Na}\left(\text{g}\right)+\text{I}\left(\text{g}\right)\to {\text{Na}}^{+}\left(\text{g}\right)+{\text{I}}^{-}\left(\text{g}\right)$

$\text{Na}\left(\text{g}\right)+\text{I}\left(\text{g}\right)\to {\text{Na}}^{-}\left(\text{g}\right)+{\text{I}}^{+}\left(\text{g}\right)$

(b) $\text{Rb}\left(\text{g}\right)+\text{Br}\left(\text{g}\right)\to {\text{Rb}}^{+}\left(\text{g}\right)+{\text{Br}}^{-}\left(\text{g}\right)$

$\text{Rb}\left(\text{g}\right)+\text{Br}\left(\text{g}\right)\to {\text{Rb}}^{-}\left(\text{g}\right)+{\text{Br}}^{+}\left(\text{g}\right)$

Explain why ${\text{Na}}^{+}{\text{I}}^{-}$ and ${\text{Rb}}^{+}{\text{Br}}^{-}$ form in preference to ${\text{Na}}^{-}{\text{I}}^{+}$ and ${\text{Rb}}^{-}{\text{Br}}^{+}$ .