eli5-Why do you feel that ‘coldness’ after using hand sanitizer



In: Chemistry

because alcohol evaporates so quickly, when it evaporates it cools your hand or the surface its on using evaporative cooling.

Alcohol evaporates very easily at room temperature.

However to evaporate takes a bunch of energy, this energy is pulled from your skin in the form of heat leaving them feeling cold.

The alcohol evaporates quite quickly. Evaporation is a state change from a liquid to a gas and it requires energy and the energy that is used is heat from your skin so you cool down.

This is the exact same reason you get cooled down when you sweat, the water requires energy to evaporate, it just happens at a lower rate.

The need of energy is why you need to continue to heat water at boiling temperature for it to continue boiling. Boiling is evaporation but at an unlimited rate and it requires energy to and will cool down the water below the boiling temperature if you remove it from the heat source.

This is because of the “heat of vaporization”. A liquid such as water for example doesn’t smoothly absorb heat and rise in temperature until it gets to boiling temperature and then suddenly becomes vapor. Instead there is an amount of energy that the water absorbs without changing in temperature before it makes the phase change. For water this is actually five times more energy than heating it from 0 to 100 Celsius!

Alcohol in the hand sanitizer will evaporate easily at room temperature but it needs to absorb that heat energy required to change into a vapor from the surrounding area. That heat being pulled out of your hands feels cold.