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Chapter 10: Problem 23

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

Expert verified
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

01

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.
02

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.
03

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.
04

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.
05

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.

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