Question

Ethanol (grain alcohol) has a molar heat of vaporiza tion of \(39.3 \mathrm{~kJ} / \mathrm{mol}\). Ethyl acetate, a common solvent. has a molar heat of vaporization of \(32.5 \mathrm{~kJ} / \mathrm{mol}\). Which of these substances has the stronger intermolecular attractions?

Short answer

Ethanol has the stronger intermolecular attractions.

Step-by-step solution

Identify the Relationship

The molar heat of vaporization is the amount of energy needed to vaporize one mole of a liquid at its boiling point. A higher molar heat of vaporization implies stronger intermolecular attractions because more energy is required to overcome these forces.

Compare Molar Heats of Vaporization

Ethanol has a molar heat of vaporization of 39.3 kJ/mol, while ethyl acetate has a molar heat of vaporization of 32.5 kJ/mol. Therefore, ethanol requires more energy per mole to vaporize.

Determine Substance with Stronger Intermolecular Attractions

Since ethanol has a higher molar heat of vaporization than ethyl acetate, it indicates that ethanol has stronger intermolecular attractions.

Key concepts

Intermolecular Attractions

Understanding intermolecular attractions is crucial when exploring the behaviors of different substances. These attractions are the forces that hold molecules together in the liquid state and are also responsible for the phase changes from liquid to gas and vice versa. In the context of the vaporization of liquids, a higher molar heat of vaporization typically signals stronger intermolecular forces at play.

The essential types of intermolecular forces include London dispersion forces, dipole-dipole interactions, and hydrogen bonding. The strength of these forces largely dictates the energy required to separate molecules during the process of vaporization. For instance, hydrogen bonding, which is a strong type of dipole-dipole interaction, is found in molecules where hydrogen is directly connected to a highly electronegative atom like oxygen, nitrogen, or fluorine.

Comprehending the relationship between these intermolecular forces and the molar heat of vaporization helps explain why some liquids boil at higher temperatures and others at lower, even under similar atmospheric conditions.

Ethanol Vaporization

When evaluating the vaporization of ethanol, a grain alcohol, it is important to focus on its relatively high molar heat of vaporization (39.3 kJ/mol). This indicates that ethanol has strong intermolecular attractions that require substantial energy to overcome. The presence of an -OH (hydroxyl) group in ethanol allows for hydrogen bonding, which is one of the strongest intermolecular forces.

By understanding the specific interactions in ethanol, it becomes clearer why this substance requires a significant amount of energy to transition from liquid to gas. This energy is directly related to the strength and number of hydrogen bonds among ethanol molecules which must be broken for vaporization to occur. In an educational context, emphasizing the link between hydrogen bonding and vaporization energy can enhance students' grasp of the physical properties of alcohols and their behavior during phase changes.

Ethyl Acetate

Ethyl acetate is commonly used as an organic solvent and has a molar heat of vaporization of 32.5 kJ/mol. This value is less than that of ethanol, suggesting that ethyl acetate's intermolecular attractions are not as strong as those in ethanol. Ethyl acetate does not have the capacity for hydrogen bonding like ethanol, due to the absence of a direct bond between hydrogen and a highly electronegative atom.

The intermolecular forces in ethyl acetate are primarily composed of van der Waals forces, including London dispersion forces and possible dipole-dipole interactions, due to the polar nature of the ester group. These forces are weaker compared to hydrogen bonds, accounting for the lower amount of energy required to vaporize ethyl acetate. In educational materials, highlighting the differences between the molecular structures of ethanol and ethyl acetate can aid students in understanding how varying intermolecular forces affect vaporization and boiling points.