Question

identify the compound with the highest vapor pressure.

1-pentanol, \\(\text{ch}_3\text{ch}_2\text{ch}_2\text{ch}_2\text{ch}_2\text{oh}\\)
pentane, \\(\text{ch}_3\text{ch}_2\text{ch}_2\text{ch}_2\text{ch}_3\\)
butane, \\(\text{ch}_3\text{ch}_2\text{ch}_2\text{ch}_3\\)
1-hexylamine, \\(\text{ch}_3\text{ch}_2\text{ch}_2\text{ch}_2\text{ch}_2\text{ch}_2\text{nh}_2\\)

Explanation:

Relate vapor pressure to intermolecular forces

Vapor pressure is inversely proportional to the strength of intermolecular forces (IMFs). The compound with the weakest IMFs will have the highest vapor pressure because its molecules can escape into the gas phase most easily.

Analyze the intermolecular forces of each option

• 1-pentanol (\(\text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2\text{CH}_2\text{OH}\)): Exhibits strong hydrogen bonding due to the \(\text{-OH}\) group, along with London dispersion forces.
• 1-hexylamine (\(\text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2\text{CH}_2\text{CH}_2\text{NH}_2\)): Exhibits hydrogen bonding due to the \(\text{-NH}_2\) group, along with London dispersion forces.
• pentane (\(\text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2\text{CH}_3\)): Nonpolar hydrocarbon exhibiting only London dispersion forces.
• butane (\(\text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_3\)): Nonpolar hydrocarbon exhibiting only London dispersion forces.

Compare the nonpolar compounds

Both pentane and butane only have London dispersion forces. Since butane has a smaller molecular weight and smaller surface area than pentane, its London dispersion forces are weaker. Therefore, butane has the weakest overall intermolecular forces and the highest vapor pressure.

Answer:

• 1-pentanol, \(\text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2\text{CH}_2\text{OH}\)
• pentane, \(\text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2\text{CH}_3\)
• butane, \(\text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_3\) (Correct answer)
• 1-hexylamine, \(\text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2\text{CH}_2\text{CH}_2\text{NH}_2\)