Heat Capacity and Water

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Water has a high heat capacity—it absorbs a lot of heat before it begins to get hot. You may not know how that affects you, but the heat capacity of water has a huge role to play in the Earth's climate and helps determine the habitability of many places around the globe.

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A beach in Scilly, England, showing tropical plants

The heat capacity of water is partially responsible for the mild climate along Englands southwestern shore. There are beaches, as at Porthcressa Beach in Scilly, where tropical plants grow.

Credit: Wikimedia

Specific heat is defined by the amount of heat needed to raise the temperature of 1 gram of a substance 1 degree Celsius (°C). Water has a high specific heat capacity which we'll refer to as simply "heat capacity", meaning it takes more energy to increase the temperature of water compared to other substances. This is why water is valuable to industries and in your car's radiator as a coolant. The high heat capacity of water also helps regulate the rate at which air changes temperature, which is why the temperature change between seasons is gradual rather than sudden, especially near the oceans.

This same concept can be expanded to a world-wide scale. The oceans and lakes help regulate the temperature ranges that billions of people experience in their towns and cities. Water surrounding or near cities take longer to heat up and longer to cool down than do land masses, so cities near the oceans will tend to have less change and less extreme temperatures than inland cities. This property of water is one reason why states on the coast and in the center of the United States can differ so much in temperature patterns. A Midwest state, such as Nebraska, will have colder winters and hotter summers than Oregon, which has a higher latitude but has the Pacific Ocean nearby.

If you leave a bucket of water outside in the sun in summer it will certainly get warm, but not hot enough to boil an egg. But, if you walk barefoot on the black asphalt of a street in the southern portion of the United States in August, you'll burn your feet. Dropping an egg on the metal of my car hood on an August day will produce a fried egg. Metals have a much lower specific heat capacity than water. If you've ever held onto a needle and put the other end in a flame you know how fast the needle gets hot, and how fast the heat is moved through the length of the needle to your finger. Not so with water.


Why heat capacity is important

Fish pond

Credit: LENA15 | pixabay.com

The high heat capacity of water has a great deal to do with regulating extremes in the environment. For instance, the fish in this pond are indeed happy because the heat capacity of the water in the pond means the temperature of the water will stay relatively the same from day to night. They don't have to worry about either turning on the air conditioner or putting on their woolen flipper gloves. (Also, for happy fish, check out our page on Dissolved Oxygen.)

Lucky for me, you, and the fish in the pond to the right, water does indeed have a very high heat capacity. One of water's most significant properties is that it takes a lot of heat to it to make it get hot. Precisely, water has to absorb 4,184 Joules of heat (1 calorie) for the temperature of one kilogram of water to increase 1°C. For comparison sake, it only takes 385 Joules of heat to raise 1 kilogram of copper 1°C.

If you'd like to learn more about heat capacity even at the molecular level, check out this video on the specific heat of water from Khan Academy.