Question

four different liquid compounds in flasks at 20°c are represented above. the table below identifies the compounds. flask c shows the most particles in the vapor phase. which of the following is not shown in the model but best helps to explain why flask c must contain pentane?

name	chemical formula	boiling point (°c)
hexane	ch₃ch₂ch₂ch₂ch₂ch₃	69
heptane	ch₃ch₂ch₂ch₂ch₂ch₂ch₃	98
octane	ch₃ch₂ch₂ch₂ch₂ch₂ch₂ch₃	126

a the random motion of the particles within the liquids
b the relative speeds of the vapor particles in each flask
c the strength of the intermolecular forces between the particles in the liquids
d the structural formula of the molecules of the liquid and vapor in each flask

Explanation:

The vapor - liquid equilibrium and the amount of vapor present depend on the intermolecular forces. Compounds with weaker intermolecular forces have higher vapor pressures at a given temperature. Pentane has weaker intermolecular forces (London dispersion forces) compared to hexane, heptane, and octane due to its shorter carbon - chain length. This results in more particles in the vapor phase at 20°C. The strength of intermolecular forces is the key factor in explaining why flask C (with most vapor particles) contains pentane. The random motion of particles in the liquid (A) and the relative speeds of vapor particles (B) do not directly explain why a particular compound is in flask C. The structural formula (D) is shown in the table and is not something not shown in the model that helps explain the situation.

Answer:

C. The strength of the intermolecular forces between the particles in the liquids