Specific Heat of Water

As you drive through many parts of the country that have sufficient sunlight, it is not usual to see solar collectors on roof tops of houses. You can even find houses built with a southerly wall made up of containers of water to capture heat for warming a house during the winter. This use of water is tied to its high specific heat.

Specific heat is defined as the amount of heat that must be absorbed or lost for one gram of substance to change 1^o Celius (not Fahrenheit). Another way to think of specific heat is the how well a substance resists changing its temperature. Water has a high specific heat because it takes 1 calorie of energy to raise the temperature of 1 gram of water 1 degree Celsius. Only ammonia has a higher specific heat; it takes 1.23 calories to raise its temperature 1^oC. For comparison, iron has a much lower specific heat. It takes 0.1 calorie of energy to raise the temperature of 1 gram of iron 1 degree Celsius. That is why you get burned easily by a hot pan when cooking.

Specific heat is a function of hydrogen bonds. Heat is needed to break hydrogen bonds and increase molecular motion. As hydrogen bonds are formed, heat is released. One calorie of energy only causes small changes in the temperature of water. Because of its high specific heat, water has a stabilizing effect on climate. Take the shores of Kitty Hawk, North Carolina, where the climate is much milder than it is in the middle of Kansas. During the day, water absorbs much heat. During the night it releases this heat and keeps the air warm. On a large scale, the temperature of the oceans is fairly stable. This means that surface temperatures stay well within the range that life can exist.

• How does an ice cube cool a drink?
• Why does sweating cool you down?
• Why is ammonia gas used in refrigeration plants such as those that make ice cubes?

Have you ever entered a greenhouse on a hot day and noticed how cool the air is? Chances are the outside air is being pulled over a layer of water before it enters the greenhouse.

• Why does this cool down a greenhouse?
• What problems would you have regulating your body temperature if you were not made up of water, but were made up of a liquid that has a lower specific heat?
• The chemical reactions in your cells generate enough heat to kill the cells. Why don't your cells self destruct?
• What arguments can you postulate to explain the possibility of life on Mars? 

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