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What Is the Specific Heat of Water? How Is It Special?

Posted by Melissa Brinks | May 15, 2019 2:00:00 PM

General Education

 

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If you’ve ever walked along a beach on a sunny day and dipped your toes in the water to cool them off after the hot sand, you’ve taken advantage of the specific heat of water.

Despite how it may sound, specific heat doesn’t refer to the exact temperature of something. It’s a larger scientific concept that has to do with the energy it takes to heat a substance up. As you might have noticed from the example, not all substances warm up at the same rate—hence the different temperatures of the sand and water.

Water’s specific heat is one of its most interesting characteristics. In this article, we’ll be covering what specific heat is, what equation you use to find specific heat, and why water’s specific heat is so high.

 

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 The stove, pot, water, and steam all have different specific heats. 

 

What Is Specific Heat?

Specific heat is a measure of heat capacity, or how much heat a material can store when changing temperature. A high heat capacity means that a substance can absorb a lot of heat before registering a change in temperature—think about how long it takes for a pot to get warm to the touch on the stove versus how long it takes the water inside to get warm. That means that water has a higher heat capacity—it can store more heat before changing in temperature.

Specific heat refers to the exact amount of heat needed to make one unit of mass of a substance one degree warmer. Returning to our example, specific heat would identify exactly how much heat is required to make one unit of water, such as one cup, one degree warmer.

Because heat is really a measure of energy transfer, it’s more accurate to say that specific heat is actually a statement of how much energy a substance can absorb before a one-degree change in temperature.

Specific heat is typically measured in Joules and kilojoules per one gram of mass, with Celsius as a measure of temperature. Kilograms and Fahrenheit may be used, but it’s rarer.

A substance’s specific heat can be affected by temperature and pressure, so specific heat is typically determined at constant temperature and pressure, typically 25 degrees Celsius.


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What Is the Equation for Specific Heat?

The equation to calculate specific heat is:

$$Q = s × m × ΔT$$

$Q$ represents the amount of heat, $s$ the specific heat (${\Joules}/{\gram * °\Celsius}$), m the mass of the substance in grams, and $ΔT$ the observed change in temperature.

 

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Different kinds of water, such as seawater, may have different specific heat.

 

What Is the Specific Heat of Water?

Some substances heat up quickly, while other substances heat up slowly. Water is one of the latter—it has a high specific heat capacity because it requires more energy to raise the temperature.

Water has a specific heat capacity of 4182 J/kg°C. Because water is such an important and common substance, we even have a special way to identify the amount of energy it takes to raise one gram of water by one degree Celsius—a Calorie. This is different from the kind of calorie we talk about in food. That kind of calorie is equivalent to 1,000 Calories, which is why food-related calories are also sometimes referred to as kilocalories, or kcals.

The specific heat of water is quite a bit higher than many other common substances. For example, the specific heat of iron is 449 J/kg°C, sand is 830 J/kg°C, and oak timber is 2400 J/kg°C.

That’s because water, comprised of two hydrogen atoms and one oxygen atom, is electronegative. An electronegative atom is more likely to draw electrons to itself, because one side of the atom will have a partially positive charge and the other will have a partially negative charge. The opposite-charged sides are naturally drawn to one another, forming a weaker hydrogen bond. That’s why water is able to flow past itself, but also bond together—it’s constantly forming and breaking these bonds.

These bonds are also why liquid water has a high specific heat. Any energy put toward heating water is split between breaking the bonds and heating the water. Because of this, it takes more energy to heat water than it does other substances.

For example, if you’re at the beach on a sunny day, you’ll notice that the sand is often quite hot to walk on, but the water always feels cool, even in the shallows. That’s because sand has a lower specific heat capacity—it takes less energy to raise the temperature by one degree. Because water has a high heat capacity, it requires more energy to raise the temperature by one degree. The sun puts out a more or less constant rate of energy, which heats up sand more quickly and water more slowly.

 

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 Sand has a much lower specific heat than water—that's why it gets hot so fast!

 

Specific Heat Table

If you’re not already familiar with Joules and Calories, these numbers might seem a little abstract. Take a look at this table to familiarize yourself with some common specific heats according to both Joules and Calories, and compare those to what you know of how these substances heat up!

Material Specific Heat in J/kg°C Specific Heat in Cal/gram°C
Gold 129 0.031
Air 1005 0.24
Leather 1500 0.36
Olive oil 1790 0.43
Paper 1336 0.32
Table Salt 880 0.21
Quartz Sand 830 0.19
Steel 490 0.12
Liquid Water 4182 1.00
Wood 1300 - 2400 0.41

 

 

What’s Next?

If the specific heat of water has you all fired up about chemistry, AP chemistry may be for you! Check out this AP chemistry syllabus to learn more about what topics will be covered.

Or maybe you're already in AP chemistry and you're looking for some tips and tricks for how to ace your exam. Check out this guide to the AP chemistry exam for everything you need to know!

If you're not quite ready for the exam but you need a little extra boost in your AP chemistry course, this AP Chemistry study guide may be just what you're looking for.

 

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Melissa Brinks
About the Author

Melissa Brinks graduated from the University of Washington in 2014 with a Bachelor's in English with a creative writing emphasis. She has spent several years tutoring K-12 students in many subjects, including in SAT prep, to help them prepare for their college education.



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