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### Course: Biology archive>Unit 2

Lesson 3: Temperature and state changes in water

# Heat of vaporization of water and ethanol

Heat of vaporization of water and ethanol.

## Want to join the conversation?

• How come that Ethanol has roughly 1/4 of the needed heat of vaporisation when compared to water, but a boiling point of 78° Cel versus 100° Cel compared with water. This doesn't make intuitive sense to me, how can I grasp it?
• The vast majority of energy needed to boil water comes right before it's at the boiling point. It takes way less energy to heat water to 90ºC than to 100ºC, so the relative amounts of energy required to boil ethanol vs. water are actually as large as stated in the video. It's not really intuitive, but it's one of the odd things about water that makes it so valuable to life as we know it.
• Doesn't the mass of the molecule also affect the evaporation rate. The ethanol molecule is much heavier than the water molecule. Shouldn't this dimimish the advantage of lower bonding in ethanol against water?
• Nope, the mass has no effect. CO2 (gas) for example is heavier than H2O (liquid). it is about how strong the intermolecular forces are that are holding the molecules together.
• At , why did Sal say that the molecule (ethanol) will have to distribute charge. Are partial charges distributed?
• Can water vaporize in a vacuum?
• What is the boiling point of water in a vacuum?
• In a vacuum water will instantly boil as long as it is not frozen.
• At Sal says "this tells you you have an alcohol". What exactly about the structure of ethanol tells you this?
• Good question. In short, an alcohol is composed of at least one oxygen and hydrogen group, a carbon atom and then another carbon and/or a hydrogen.

The structure of an alcohol is composed of a hydroxyl group (Bonded oxygen and hydrogen) that is also bonded to a carbon atom. The carbon atom is then bonded to another carbon atom and/or hydrogen atom. In this case, the oxygen is bonded with the hydrogen, forming a hydroxyl group. The oxygen is then bonded to another carbon. The carbon is bonded with 2 hydrogen and another carbon, and the other carbon is bonded to another 2 hydrogen atoms. This forms abides the guidelines. There is one oxygen, 5 hydrogen, and 2 carbon. This makes an alcohol.
• What are the diagrams called?
• a simplified drawing showing the appearance, structure, or workings of something; a schematic representation.
• How does the heat of vaporization impact the effectiveness of evaporative cooling?

Ethanol evaporates at a lower temperature meaning it will evaporate sooner, but will use up less energy in doing so. Does anyone know if this makes it more or less efficient than water? or does it even make a difference?
• Heat of vaporization directly affects potential of liquid substance to evaporate.

Ethanol is more efficient since it evaporates sooner.

`Heat of vaporization↑ => evaporate cooling↓andHeat of vaporization↓ => evaporate cooling↑`