The boiling point of a liquid is the temperature at which it transforms into a gaseous state. For pure ethanol, the alcohol found in alcoholic beverages, this occurs at approximately 78.37°C (173.1°F) at standard atmospheric pressure. This temperature indicates the point where its molecules gain enough energy to overcome liquid forces and escape as a gas.
Why Alcohol Boils at a Lower Temperature
Ethanol boils at a lower temperature than water due to differences in their intermolecular forces, which are the attractive forces between molecules. Water molecules form strong hydrogen bonds because each water molecule has two hydrogen atoms capable of forming these bonds. These strong attractions require substantial energy to break, explaining water’s high boiling point of 100°C (212°F).
Ethanol molecules also form hydrogen bonds, but they are weaker compared to those in water. This is partly because ethanol molecules have only one hydrogen atom involved in hydrogen bonding. Less energy is needed to overcome these weaker forces, allowing ethanol to boil at a lower temperature.
How External Factors Affect Boiling Point
The stated boiling point for ethanol is for a pure substance under standard atmospheric pressure, but real-world conditions can alter this temperature. Atmospheric pressure, for instance, significantly influences a liquid’s boiling point. At higher altitudes, where atmospheric pressure is lower, liquids boil at reduced temperatures because there is less external pressure pushing down on the liquid’s surface. Conversely, in environments with higher pressure, the boiling point of alcohol will increase.
The purity of alcohol also plays a role in its boiling temperature. Alcohol is frequently found in mixtures, especially with water. When alcohol is mixed with other substances, the boiling point of the mixture will differ from that of pure ethanol or the other component. For example, a mixture of alcohol and water will have a boiling point somewhere between 78.37°C and 100°C, depending on the concentration of each liquid.
Practical Uses and Common Beliefs
Understanding alcohol’s boiling point has practical implications in cooking and spirit production. Many believe all alcohol “cooks off” completely during cooking. While alcohol begins to evaporate at approximately 78°C (173°F), it does not disappear entirely from food.
The amount of alcohol that remains in a dish depends on factors such as cooking time, temperature, and the surface area of the cooking vessel. Studies show that even after significant cooking times, a percentage of the alcohol can still be present; for example, 40% might remain after 15 minutes of cooking, and 5% could still be there after two and a half hours.
The difference in boiling points between alcohol and water is the fundamental principle behind distillation, a process used to separate and concentrate alcohol. In distillation, a fermented mixture containing alcohol and water is heated. Since ethanol has a lower boiling point than water, it vaporizes first. These alcohol-rich vapors are then collected and cooled, causing them to condense back into a liquid with a higher concentration of alcohol. This method allows for the creation of spirits and other concentrated alcoholic products.