High Specific Heat Capacity of Water

Note the especially high specific heat capacity of water. The specific capacity of water is about 5 times larger than that of sand (or granite), meaning that for the same energy transfer, a of water changes temperature about one fifth that of a of sand. This has important consequences to the weather and temperature in different areas on Earth.

 
  Fig. 3-5 Hong Kong has almost the same latitude as Nagpur in India, but the daily temperature change in Hong Kong is much smaller than that of Nagpur. This is closely related to the high specific heat capacity of water.

For example, Hong Kong and Nagpur in India has almost the same latitude, but the daily temperature range is very different between the two cities. For a typical day in October, the daily temperature range in Nagpur is 12.8 while for Hong Kong is only about 4.8 .

Flash animation: Large specific heat capacity of water

The main reason for the difference is that Hong Kong is a coastal city surrounded by a large mass of water while Nagpur is an inland city surrounded by large mass of land. During daytime, the temperature of both cities rises because of the heating of the sun. However, water is heated up much slower than land. Thus during daytime the coastal city is surrounded by cooler water, but the inland city is surrounded by hot land. As a result, the coastal city will have a lower temperature. When the sun sets, water cools down much slower than land. Thus during nighttime the coastal city is surrounded by warmer water, but the inland city is surrounded by cold land. The coastal city will have a higher temperature during nighttime. The combined effect is that the coastal city has a daily temperature change much smaller than that of the inland city.


 
  Fig. 3-6 Water is used to cool down the temperature of the reactor in a nuclear power plant.

Water takes up a lot of heat with a small temperature rise. This makes water an ideal coolant. Water is used to cool down the engine of motor cars. When we have a fever, we use cold water bag to help lowering our body temperature. Nuclear power plants are usually built in coastal areas where an abundant supply of water is available for cooling the reactors.

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