Question

If the back of your hand is moistened with alcohol, you will find that it rapidly becomes dry. Why is it that while it is drying, your hand feels cool ?

Answer 1

• The alcohol on our hands absorbs its latent heat of vaporization from the surface of our hands and evaporates. Drawing heat and therefore, cooling our hands in the process.
• Alcohol is a highly volatile liquid. hence it gets easily evaporated at normal temperatures.
• Alcohols are relatively low volatile compounds as they possess hydrogen bonds between the molecules, resulting in more energy required to separate the molecules when compared to alkanes.
• But the boiling point is very low when compared to water for ethanol it is ${78.5}^{o}C$.
• So when alcohol moistens the hands, it absorbs the latent heat of vaporization from the surface of the body.
• It absorbs the heat of the body and utilizes the energy to convert its state of liquid to a gaseous state.
• Hence, As the hand loses heat to alcohol, it feels cool. this is an example of cooling by evaporation.