Question

When a person has a severe fever, one therapy used to reduce the fever is an "alcohol rub." Explain how the evaporation of alcohol from a person's skin removes heat energy from the body.

Short answer

An alcohol rub works by using the process of evaporation, where alcohol changes its state from liquid to gas on the person's skin, absorbing heat energy in the process. Alcohol has a low heat of vaporization and evaporates faster compared to other liquids, making it more efficient in cooling the body. As the alcohol evaporates, it causes a cooling effect on the skin, which lowers the body's temperature and helps reduce fever.

Step-by-step solution

Understand the process of evaporation

The first step in understanding how an alcohol rub works is to be familiar with the concept of evaporation. Evaporation is a process in which a liquid changes its state to a gas at a temperature below its boiling point. This happens due to the movement of the liquid's molecules. The molecules on the surface of the liquid have enough energy to escape the intermolecular forces that hold them together, turning into gas. In our case, alcohol in contact with the skin will evaporate.

Define the heat of vaporization

The heat of vaporization is the amount of heat energy required to transform a certain amount of a substance from its liquid phase to its vapor phase at a constant temperature. In the case of an alcohol rub, heat energy is absorbed by the alcohol from the person's skin in order for the alcohol to evaporate. This is called endothermic process since it needs heat energy to be accomplished.

Understand the cooling effect caused by evaporation

When alcohol evaporates, it absorbs heat energy from its surroundings, which in this case is the person's skin. Since heat energy is being transferred from the skin to the evaporating alcohol, the temperature of the skin will decrease, resulting in a cooling effect. This process helps in lowering the fever of the person and providing relief from the high body temperature. The cooling effect is more noticeable when there is an increased surface area for the evaporation, such as when the alcohol is rubbed on a large area of the skin.

Explain the effectiveness of alcohol in removing heat energy

Alcohol has a relatively low heat of vaporization compared to other liquids, such as water. This means that it requires less heat energy to evaporate alcohol, allowing it to absorb heat more efficiently and produce a more significant cooling effect. Additionally, alcohol evaporates at a faster rate than water due to its lower boiling point, which also contributes to its effectiveness in cooling the body during an alcohol rub.

Summarize how alcohol rub reduces fever

In conclusion, during an alcohol rub, the alcohol evaporates from the person's skin, absorbing heat energy in the process. This results in a cooling effect on the skin, lowering the body's temperature and helping reduce fever. The low heat of vaporization and faster evaporation rate of alcohol make it an efficient substance for this purpose.

Key concepts

Heat of Vaporization

The heat of vaporization refers to the energy required to turn a liquid into a gas at a constant temperature. Imagine it as the energy needed to "break free" from the liquid state. In the case of alcohol rubs, this concept becomes very handy. When alcohol is applied to the skin, it begins to evaporate. As it does so, it absorbs heat from the skin, which is essentially the source of energy it needs. This energy transfer is part of why we feel cooler when alcohol evaporates from the skin.
Alcohol specifically has a lower heat of vaporization when compared to water. This means that it can evaporate with relatively less energy. This makes it a good choice for quickly reducing skin temperature, such as when treating fevers. The low energy requirement for alcohol's vaporization supports its role in heat absorption and subsequent cooling.

Endothermic Process

An endothermic process is a reaction that requires the absorption of heat. Applying an alcohol rub exemplifies this. As alcohol transforms from liquid to gas, it absorbs heat from the environment – here, the skin. This absorption occurs because alcohol needs energy to change states, which it "pulls" from surrounding sources.
This need for energy consumption classifies the rubbing of alcohol on the skin as an endothermic process. The body effectively surrenders some of its body heat to the evaporating alcohol, which in turn facilitates fever reduction. Understanding this process is key to grasping why alcohol rubs are effective therapies for managing fever.

Cooling Effect

The cooling effect is the result of evaporation, specifically when a liquid absorbs heat as it becomes gas. When alcohol is rubbed on the skin, it absorbs the heat required to evaporate. This transfer cools the skin because the heat moves from the skin to the evaporating alcohol.
The cooling effect is an essential component of how an alcohol rub functions to reduce fever. As the heat leaves the skin, the body's temperature decreases, providing a sense of relief from the feverish heat. Additionally, alcohol's rapid evaporation due to its low boiling point further enhances this cooling sensation, making it a popular choice for immediate relief in fever treatment. The larger the area of skin covered and the more alcohol used, the more pronounced the cooling effect will be, aiding in effective fever management.