Question

The main reason why H2CO has a higher vapor pressure at a given temperature when compared to CH3OH is that H2CO

Answer 1

Formaldehyde (H2CO) has a higher vapor pressure than methanol (CH3OH) due to weaker intermolecular forces, as methanol can form stronger hydrogen bonds which formaldehyde cannot, leading to a lower vapor pressure for methanol.

Step-by-step explanation:

The main reason why H2CO (formaldehyde) has a higher vapor pressure at a given temperature compared to CH3OH (methanol) is because of the different types of intermolecular forces (IMFs) present in each compound. Methanol can form hydrogen bonds due to its -OH group, which are much stronger than the dipole-dipole interactions and London dispersion forces present in formaldehyde.

Despite methanol and formaldehyde having similar molar masses, the stronger hydrogen bonding in methanol means that more energy is needed to escape from the liquid phase, resulting in a lower vapor pressure for methanol compared to formaldehyde.

Answer 2

Cannot form hydrogen bonds to its neighbours.

Step-by-step explanation:

The strongest intermolecular forces in H₂CO are dipole-dipole attractions between the polar C=O bonds in nearby molecules.

The strongest intermolecular forces in CH₃OH are strong hydrogen bonding attractions between the O-H group in one molecule and the O atom in a nearby molecule.

Since H₂CO molecules have weaker intermolecular forces than methanol, more of them can escape from the liquid to the vapour phase.

Thus, CH₂O has a higher vapour pressure than methanol.