Boiling Points – Quiz

The alcohol is the only molecule that contains H-bonding.

The bigger the intermolecular forces the more difficult it is to evaporate and therefore the lower the vapor pressure.

Density for gases is determined through their molar mass, the lower the molar mass, the lower the density. This is due to Avogadro’s law that states that under the same conditions of temperature and pressure, equal volumes of different gases contain an equal number of moles.

This is because the boiling point of a compound generally increases with increasing intermolecular forces (such as hydrogen bonding, dipole-dipole interactions, and London dispersion forces) between its molecules.

Out of the given compounds, CH₄ has only weak London dispersion forces and no hydrogen bonding or dipole-dipole interactions. NH₃ has stronger (polar) dipole-dipole forces and can also form hydrogen bonds between its molecules, making it have a higher boiling point than CH₄. H₂O has even stronger hydrogen bonding between its molecules, and thus it has a higher boiling point than NH₃.

H₂O has a higher boiling point than HF because it contains twice as many H- bonds, despite these being individually weaker.

The increase in boiling point is resultant from the increase in the carbon chain, thus from an increase in the dispersion forces (induced dipoles – induced dipoles)

H₂O has hydrogen bonding, therefore it would have the highest boiling point. The other three hydrides all have dipole-dipole interactions. Therefore the bigger the molecule the more electrons present, therefore the more dipole-dipole interaction that will be present, increasing the boiling point as the element gets bigger (going down the group). This would mean that H₂S would have the lowest boiling point.

All of the molecules only have induced dipole-induced dipole interactions as their intermolecular forces. This means that F₂ should be closest to Ar in terms of boiling points since F₂ has the closest number of electrons to Ar. (For induced dipole interactions the number of electrons are responsible for the number of induced dipoles.)

2-propanol has a H attached to an O, resulting in hydrogen bonding, the strongest type of intermolecular forces, whilst propanone has no hydrogen bonding, resulting in a lower boiling point when compared to water.

The lowest boiling point will be the compound that only has induced dipole – induced dipoles. Propane has induced dipoles only, which would result in the lowest boiling point.

The substance that boils first will be the substance that has the lowest boiling point.