Select the substance in each pair that should have the higher boiling point. In each case identify the principal intermolecular forces involved and account briefly for your choice. (a) \(\mathrm{K}_{2} \mathrm{~S}\) or \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{~N},\) (b) \(\mathrm{Br}_{2}\) or \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}\)

Short Answer

Expert verified
For pair (a), \(\mathrm{K}_{2} \mathrm{~S}\) should have the higher boiling point primarily due to its stronger ionic bonds. For pair (b), \(\mathrm{Br}_{2}\) should have the higher boiling point due to its stronger London dispersion forces

Step by step solution

01

Compare the substances in pair (a)

Let's start by comparing \(\mathrm{K}_{2} \mathrm{S}\) and $\left(\mathrm{CH}_{3}\right)_{3}\mathrm{N}$. \(\mathrm{K}_{2} \mathrm{~S}\) is an ionic compound and thus its principal intermolecular force would be the ionic bond, which is typically stronger than any type of intermolecular force present in covalent compounds. Contrarily, $(\mathrm{CH}_{3})_{3} N$ is a covalent compound with dipole-dipole forces as its primary intermolecular force since the nitrogen atom makes the molecule polar. Thus, \(\mathrm{K}_{2} \mathrm{~S}\) should have the higher boiling point.
02

Compare the substances in pair (b)

Now let's compare \(\mathrm{Br}_{2}\) and $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}$. Both are covalent compounds and the intermolecular forces are London dispersion forces (induced dipole-dipole interaction) for both. However, \(\mathrm{Br}_{2}\) is a much larger molecule with more electrons, leading to stronger dispersion forces. Thus, \(\mathrm{Br}_{2}\) should have the higher boiling point.

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