Why alcohol evaporates

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We could end up blogging about it! Skip to content. Rubbing Alcohol — What is it? Evaporative Cooling To explain this concept, we have to understand evaporation in general. But what does this have to do with rubbing alcohol? Next Post: Writing on the Wall.

Home Archives About Contact. Media Player Error Update your browser or Flash plugin. The alcohol feels cold because of a process called evaporative cooling. When something gets warmer its molecules move faster. Heat and Movement When a liquid evaporates, or changes into a gas, the fastest molecules break loose from the liquid and fly off on their own. Source Lohner, S. Chilling Science: Evaporative Cooling with Liquids.

Blowing on your wet hand helps the water and alcohol to evaporate. The airflow will also support the heat transfer away from your skin.

You should have noticed that your skin feels much cooler when you put the rubbing alcohol on your hand compared with the water. The water and the alcohol will start to evaporate once you start blowing on your hand. Compared with water, alcohol has a lower heat of evaporation.

That means that for the same amount of liquid, more heat transfer occurs during the evaporation of water compared with the alcohol. This does not fit your observation that alcohol has a greater cooling effect than water, however.

The reason for that is that the amount of heat transfer also depends on the evaporation rate. As alcohol evaporates at a much faster rate compared with water due to its lower boiling temperature 82 compared to degrees C , it is able to carry away more heat from the skin.

This means for a given amount of time much more alcohol evaporates than water. You probably noticed this also when you did the extra activity of putting the same amount of alcohol and water outside in the sun and monitored their evaporation rates.

Other factors that influence evaporation rates are the surface area, temperature and airflow. Cleanup Flush any unused rubbing alcohol down the sink with plenty of cold water. Wash your hands with soap, and clean your work area. This activity brought to you in partnership with Science Buddies.

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See Subscription Options. Go Paperless with Digital. Key concepts Physics Evaporation Heat transfer Temperature Introduction Have you ever wondered why we sweat when our environment is hot or when we exercise? Materials Rubbing alcohol Water Two small cups or bowls Tablespoon Pipet or medical dropper Preparation Fill one small cup or bowl with one tablespoon of water.

Fill the second small cup or bowl with one tablespoon of rubbing alcohol. Procedure Suck up some water from the first bowl water using the pipet or medical dropper. Carefully drop one or two drops on the back of our hand and spread the liquid with your fingers.

When the water touches your skin, how does it feel? Blow softly over the skin area that you just covered with water. Does your skin feel any different when blowing on the water?