Hexane is a hydrocarbon (a molecule containing only carbon and hydrogen) with a molecular weight of 86.18 g/mol,

a density of 0.660 g/mL, and a boiling point of 69C .

Pentanol is an alcohol (a hydrocarbon with a "OH" group attached to one of its carbons) with a molecular weight of
88.15 g/mol, a density of 0.814 g/mL, and a boiling point of 137C .

Pentanol has the higher boiling point. Why?
A. Hydrogen bonding requires that a pentanol molecule have more energy to escape the liquid phase.
B. Pentanol is capable of hydrogen bonding, so it goes into the gas phase more easily.
C. Hexane has stronger intermolecular forces, so it boils at a lower temperature.
D. The higher molecular weight of pentanol results in a higher boiling point.
E. The dispersion forces in hexane are weaker.

What is your thinking? I will be happy to critique your thinking. Please refrain from posting under multiple names

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To understand why pentanol has a higher boiling point compared to hexane, we need to consider the intermolecular forces present in each compound.

Hexane is a nonpolar molecule due to the symmetrical arrangement of carbon and hydrogen atoms. It only has dispersion forces (also known as London forces or Van der Waals forces), which are weak attractive forces between temporary dipoles. The dispersion forces in hexane are relatively weaker compared to other intermolecular forces.

Pentanol contains an "OH" group, which introduces polarity to the molecule. The oxygen atom attracts electrons more than hydrogen and carbon atoms, creating a partial negative charge on the oxygen and partial positive charges on the hydrogen atoms. This polarity allows pentanol to have stronger intermolecular forces, specifically hydrogen bonding.

Now, we can evaluate the given options to determine the reason for pentanol's higher boiling point:

A. Hydrogen bonding requires that a pentanol molecule have more energy to escape the liquid phase.
This option is correct. Hydrogen bonding is stronger than dispersion forces, requiring more energy to overcome and break the attractive forces between pentanol molecules. As a result, pentanol has a higher boiling point.

B. Pentanol is capable of hydrogen bonding, so it goes into the gas phase more easily.
This statement is incorrect. Hydrogen bonding makes it more difficult for pentanol molecules to enter the gas phase.

C. Hexane has stronger intermolecular forces, so it boils at a lower temperature.
This statement is incorrect. Hexane only has weak dispersion forces, while pentanol has stronger intermolecular forces due to hydrogen bonding.

D. The higher molecular weight of pentanol results in a higher boiling point.
The higher molecular weight of pentanol might contribute to its higher boiling point to some extent, but it is not the primary reason. The primary factor is the presence of hydrogen bonding in pentanol.

E. The dispersion forces in hexane are weaker.
This statement is correct. Hexane only has dispersion forces, which are relatively weaker compared to the hydrogen bonding in pentanol.

Therefore, the correct answer is A. Hydrogen bonding requires that a pentanol molecule has more energy to escape the liquid phase.