Super Powered Water: Specific Heat and Heat of Vaporization

Why does cheese on pizza, fresh from the oven, burn the roof of your mouth? Blame water. In Part 2 of this series, Everyday Einstein reveals two more unique superpowers of water.

Lee Falin, PhD,
November 23, 2013
Episode #077

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pizzaHave you ever picked up a just-cooked slice of pizza fresh from the oven, taken a bite, and screamed in pain because the cheese just melted the roof of your mouth? If you have, don’t blame yourself, blame water. 

As I mentioned in a Part 1 of this series, water has a wide variety of superpowers, thanks to its ability to form hydrogen bonds. To review, water molecules are formed when one oxygen atom forms covalent bonds with two hydrogen atoms. The oxygen atom shares one electron with each hydrogen atom, which in turn share one electron each with oxygen, forming a water molecule. .

However since these shared electrons tend to spend more time on the oxygen side of the molecule, this leaves oxygen with a partial negative charge and the hydrogen atoms with partial positive charges. These partial charges allow water molecules to form hydrogen bonds or polar bonds with one another. These bonds are the source of water’s amazing powers.

Is it Hot in Here?

One of the amazing abilities granted to water by its hydrogen bonds is its high specific heat. The specific heat of something is a measurement of how much heat must be gained or lost by a substance in order to change its temperature. (Usually this is measured as the amount of heat required to change 1 gram of a substance’s temperature by 10 Celsius).

Recall that heat is a form of energy, and as we add heat to a substance, we are adding energy. As heat energy is added to a substance, the particles of that substance increase in kinetic energy, causing them to vibrate faster. The faster this vibration, the higher the substance’s temperature. 

However, water molecules form hydrogen bonds with one another. These extra bonds allow the water molecules to resist vibrating faster. Hydrogen bonds also absorb heat when they form. This means that to increase its temperature, water has to absorb a lot of heat. In fact, only ammonia (which also forms hydrogen bonds) has a higher specific heat than water. 

Water’s high specific heat doesn’t just mean that it requires a large increase of energy to heat up, it also means that it requires a large decrease of energy to cool down, almost twice as much as most carbon compounds.