Questions: Rate the molar enthalpies of vaporization of the following substances in increasing order: CH₄, C₂H₆, and C₃H₈. CH₄<C₂H₆<C₃H₈ C₃H₈<CH₄<C₂H₆ C₂H₆<CH₄<C₃H₈ CH₄<C₃H₈<C₂H₆

Solution Steps

• Molar enthalpy of vaporization is the amount of energy required to vaporize one mole of a substance at its boiling point.
• It is influenced by the strength of intermolecular forces; stronger forces require more energy to overcome.

• The substances given are methane ($\mathrm{CH}_{4}$), ethane ($\mathrm{C}_{2}\mathrm{H}_{6}$), and propane ($\mathrm{C}_{3}\mathrm{H}_{8}$).
• These are all hydrocarbons with increasing molecular size and mass.

• Larger molecules generally have stronger London dispersion forces due to increased surface area and electron cloud size.
• Therefore, as molecular size increases from $\mathrm{CH}_{4}$ to $\mathrm{C}_{3}\mathrm{H}_{8}$, the molar enthalpy of vaporization is expected to increase.

• Based on the increasing molecular size and corresponding increase in intermolecular forces, the order is: $$\mathrm{CH}_{4} < \mathrm{C}_{2}\mathrm{H}_{6} < \mathrm{C}_{3}\mathrm{H}_{8}$$

Final Answer