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

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

Transcript text: Rate the molar enthalpies of vaporization of the following substances in increasing order: $\mathrm{CH}_{4}, \mathrm{C}_{2} \mathrm{H}_{6}$, and $\mathrm{C}_{3} \mathrm{H}_{8}$. $\mathrm{CH}_{4}<\mathrm{C}_{2} \mathrm{H}_{6}<\mathrm{C}_{3} \mathrm{H}_{8}$ $\mathrm{C}_{3} \mathrm{H}_{8}<\mathrm{CH}_{4}<\mathrm{C}_{2} \mathrm{H}_{6}$ $\mathrm{C}_{2} \mathrm{H}_{6}<\mathrm{CH}_{4}<\mathrm{C}_{3} \mathrm{H}_{8}$ $\mathrm{CH}_{4}<\mathrm{C}_{3} \mathrm{H}_{8}<\mathrm{C}_{2} \mathrm{H}_{6}$

Solution

Solution Steps

Step 1: Understand the Concept of Molar Enthalpy of Vaporization

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.

Step 2: Analyze the Substances

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.

Step 3: Relate Molecular Size to Intermolecular Forces

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.

Step 4: Order the Substances by Molar Enthalpy of Vaporization

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