Question

you said that dipole - dipole forces were most important to consider in determining the boiling point of the following molecules.
based on that and the guidelines to the right, which of the following substances below should have the higher boiling point?
co (28.0 g/mol)
n₂ (28.0 g/mol)
which substance has the stronger total intermolecular forces/the higher boiling point?

1. first, look to see if the substance can hydrogen bond. if so, it likely has the strongest intermolecular forces (e.g., hf > hcl).
2. if you are comparing two molecules of very different molar masses, london dispersion forces are more important (e.g., hbr > hcl).
3. if you are comparing two molecules of very similar molar mass, dipole - dipole forces are more important. the molecule with the greater dipole - dipole forces (the greatest electronegativity difference between the atoms within the molecule) will have the greatest boiling point.

Explanation:

CO is a polar molecule with dipole - dipole forces. \(N_2\) is a non - polar molecule with only London dispersion forces. Since CO and \(N_2\) have very similar molar masses (28.0 g/mol), according to the guideline (when molar masses are similar, dipole - dipole forces are more important), the substance with dipole - dipole forces (CO) will have stronger intermolecular forces and a higher boiling point.

Answer:

CO (28.0 g/mol)