Place the following substances in order of decreasing vapor pressure at a given temperature. BeF₂ CH₃OH OF₂ A) CH₃OH OF₂ BeF₂ B) BeF₂ OF₂ CH₃OH C) OF₂ CH₃OH BeF₂ D) OF₂ BeF₂ CH₃OH E) BeF₂ CH₃OH OF₂

Question

Place the following substances in order of decreasing vapor pressure at a given temperature. BeF₂ CH₃OH OF₂ A) CH₃OH > OF₂ > BeF₂ B) BeF₂ > OF₂ > CH₃OH C) OF₂ > CH₃OH > BeF₂ D) OF₂ > BeF₂ > CH₃OH E) BeF₂ > CH₃OH > OF₂

Quizplus · Accepted Answer

Vapor pressure is determined by the ease with which a liquid's molecules can escape into the gas phase. The lower the intermolecular forces in the liquid, the higher the vapor pressure. The given substances are all different types of compounds and have different intermolecular forces. Of the three, OF₂ has the weakest intermolecular forces and therefore the highest vapor pressure. CH₃OH has hydrogen bonding, which is stronger than the intermolecular forces in OF₂, but weaker than the intermolecular forces in BeF₂. Therefore, it has a higher vapor pressure than BeF₂, but lower than OF₂. So, the correct order of decreasing vapor pressure is OF₂ > CH₃OH > BeF₂, which matches up with option C.

Place the Following Substances in Order of Decreasing Vapor Pressure