Thermal Properties of Water

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  • 0:04 What Is Water?
  • 0:31 High Specific Heat Capacity
  • 1:20 Melting, Boiling, & Density
  • 3:01 Heat of Fusion & Vaporization
  • 3:57 Lesson Summary
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Lesson Transcript
Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

Water has many unique properties that are important to life on Earth. In this lesson we will explore the thermal properties of water to gain a better understanding of how they support life.

What Is Water?

It's likely that you know water is important. But do you really understand just how important it is? If you think about it, our planet is covered with water. Your body is mostly water. In fact, you would only survive a few days without it. But you're not the only one! All living organisms need water to survive. And what makes water special is that it has some very unique thermal properties that help us, and everything else on Earth, get up and go about our day without even thinking about it.

High Specific Heat Capacity

Let's start with the specific heat capacity of water, which is the amount of heat required to raise the temperature of 1 gram of something by 1°C, or more generally, the resistance to temperature change. Water has a very high specific heat capacity, so it can absorb a lot of heat with only a small temperature change. This is why coastal areas have more consistent temperatures throughout the year. Large bodies of water absorb and store large amounts of heat from the sun, and as they cool they release it into the air. This helps protect not only life on land from extreme temperature fluctuations, but also marine life.

Water's known specific heat capacity can also help us measure energy changes in chemical reactions. Since we know how much energy it takes to change the temperature of water by 1°C, we can use water to measure the change in heat (energy) of a chemical reaction.

Melting, Boiling, & Density

Water is also special because it has a high melting point and boiling point (0°C / 32°F = melting point; 100°C / 212°F = boiling point). As a quick reminder, the melting point is the temperature at which a solid becomes a liquid and the boiling point is the temperature at which a liquid becomes a gas. Water isn't a very 'heavy' molecule, so you might think that it would melt and boil easily. Not the case! Water's hydrogen bonds hold molecules together very tightly, making it difficult to break them apart.

The melting point of a substance is also its freezing point because this is where the phase change occurs in both directions. And this leads us to our next thermal property of water, its density. This is the amount of stuff packed into a given amount of space. Density itself isn't necessarily a thermal property, but because it changes with temperature and phase, and because water's density is so unique, we need to cover it here.

Most substances become more dense as they cool because their molecules are slowing down and condensing together. Water has its own ideas about this though! Believe it or not, water actually becomes less dense as it cools! As water cools, instead of moving closer together the molecules hold each other at arm's length with those hydrogen bonds and create a nice crystalline structure. This also explains why ice floats on top of liquid water; it's less dense!

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