Which has a higher boiling temperature? Water or alcohol?

The temperature at which a liquid turns into a gas depends heavily on how strongly its individual molecules stick to one another. These "sticky" forces are known as intermolecular forces. For both water and common alcohols like ethanol, the primary force at play is a particularly strong attraction called a hydrogen bond. Although both substances share this powerful type of bond, the seemingly minor differences in their molecular structure have a major impact on their boiling points. This is why one liquid remains stable at temperatures that would cause the other to boil away.

A single water molecule (H₂O) is a master of teamwork; it is small and can form up to four hydrogen bonds with its neighbors (Review), creating a powerful and extensive network of connections. An ethanol molecule (C₂H₅OH) also has the necessary components for hydrogen bonding, but its larger hydrocarbon tail gets in the way, limiting the number and strength of these connections compared to water. This non-polar hydrocarbon section disrupts the bonding network that water can so effectively maintain.

Because the collective hydrogen bonds between water molecules are stronger and more numerous, it takes significantly more energy to pull them apart. This need for more energy translates directly to a higher boiling temperature. To turn liquid water into steam, the temperature must reach 100°C (212°F) at sea level to overcome these forces. In contrast, the less connected ethanol molecules can escape into a gaseous state at a much lower temperature of just 78°C (173°F).