Which evaporates faster water or alcohol

Molecules at a liquid's surface are attracted only "down" and "sideways" to other molecules. So it's easier to skip out at the surface than from down further in the molecular bunch. The larger the surface, the more quickly and easily molecules make their escape. Water spilled in a pool on the floor will evaporate quickly. But the same amount of water in a long-necked bottle will take its time fleeing through the small, round surface.

Why does water evaporate more slowly than alcohol and many other liquids? Water H2O molecules are strongly bound together. These "hydrogen bonds" between the atoms of neighboring water molecules make it hard for individual molecules to break free from the bunch.

So even when water has a lower molecular weight than another liquid, it may evaporate more slowly. Ethyl rubbing alcohol, with its more loosely bound molecules, evaporates almost five times as quickly as water.

When energetic molecules depart from a liquid, they leave lower-energy, lower-temperature molecules behind. In this activity you can observe this cooling power in action—ready to get cool? Background The process of changing a liquid into its gaseous state is called evaporation.

Every liquid can be turned into a gas if enough energy is added to the liquid in the form of heat. The energy needed for the transformation is known as the heat of evaporation. How much energy you need depends on factors such as the type of liquid or the surrounding temperature. If it is already very hot outside, you will need less energy to vaporize a liquid; if it is very cold, you will need more. In order to turn into a gas the molecules held together inside the liquid have to break free to get into the air.

This means the hydrogen bonds holding the molecules together need to be broken. Thus, molecules that are able to form lots of hydrogen bonds among themselves are much harder to turn into a gas and have a higher heat of evaporation. This also affects the boiling temperature of a liquid. Molecules that attract one another very strongly start to boil at higher temperatures compared with those that have weak attractions. A lower boiling point generally means a liquid will evaporate more quickly.

Water, for example, with one oxygen and two hydrogen atoms, can form two hydrogen bonds per molecule. Its heat of evaporation is 2, joules per gram, or calories per gram, and it starts boiling at degrees Celsius degrees Fahrenheit. Your body makes use of the evaporative process when sweating. Sweat, which consists of 90 percent water, starts to evaporate. The necessary heat of evaporation is extracted from the sweat itself, which leads to a heat transfer from the liquid into the gaseous state.

This results in a cooling effect called evaporative cooling that helps to maintain body temperature and cools the body down when it gets too hot. The degree of cooling is dependent on the evaporation rate and heat of evaporation. In this activity you will find out which liquid has a greater cooling power: rubbing alcohol or water.

What do you think will cool more when it evaporates? Observations and results Did you feel the cooling power of water and rubbing alcohol?

Both liquids should feel cold on your skin. 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. Acetone evaporates much faster than water, even though its molecular mass is more than three times as much. Water molecules, in the liquid and solid state, are capable of hydrogen bonding, whereas a collection of acetone molecules in the liquid state do not.

The relatively strong hydrogen bonding between water molecules slows the evaporation rate and increases the surface tension, as evidenced by acetone's flatter drop shape on the watch glass. Ethanol exhibits hydrogen bonding between ethanol molecules but does not evaporate as quickly as water. The three watch glasses are placed on the overhead projector.

A drop of water, a drop of ethanol, and a drop of acetone are placed on separate watch glasses and the rate of evaporation is observed. The drop of acetone evaporates much faster than the drop of water or the ethanol.

One day of lead time is required for this project. Acetone is very flammable. Take appropriate precautions. Potential Health Effects of acetone: Inhalation - Inhalation of vapors irritates the respiratory tract. May cause coughing, dizziness, dullness, and headache. Higher concentrations can produce central nervous system depression, narcosis, and unconsciousness. Ingestion - Swallowing small amounts is not likely to produce harmful effects.

Ingestion of larger amounts may produce abdominal pain, nausea and vomiting. Aspiration into lungs can produce severe lung damage and is a medical emergency. Other symptoms are expected to parallel inhalation. Skin Contact - Irritating due to defatting action on skin.