Which of the following substances would you predict to have the highest enthalpy of vaporization (ΔH_{vap})?

• A. Ethanol (C_2H_5OH)
• B. Water (H_2O)
• C. Acetone (C_3H_6O)
• D. Diethyl ether (C_4H_{10}O)

Answer: (B)

Verified step by step guidance

1. Understand that the enthalpy of vaporization (\( \Delta H_{vap} \)) is the amount of energy required to convert one mole of a liquid into vapor at constant temperature and pressure. It depends largely on the strength of intermolecular forces in the liquid.
2. Identify the types of intermolecular forces present in each substance: Water (\( H_2O \)) has strong hydrogen bonding due to its highly polar O-H bonds and small molecular size; Ethanol (\( C_2H_5OH \)) also has hydrogen bonding but less extensive than water; Acetone (\( C_3H_6O \)) has dipole-dipole interactions but no hydrogen bonding; Diethyl ether (\( C_4H_{10}O \)) has weaker dipole-dipole and London dispersion forces.
3. Recall that hydrogen bonding is generally stronger than dipole-dipole and London dispersion forces, so substances with hydrogen bonding tend to have higher \( \Delta H_{vap} \).
4. Compare molecular size and structure: smaller molecules with strong hydrogen bonding (like water) tend to have higher enthalpy of vaporization than larger molecules with weaker forces.
5. Conclude that water, with its extensive hydrogen bonding network and small molecular size, will have the highest enthalpy of vaporization among the given substances.