Heat Capacity

Heat capacity (often abbreviated Cp) is defined as the amount of heat required to raise the temperature of a given mass of a substance by one degree Celsius. Heat capacity may also be defined as the energy required to raise the temperature of one mole of a substance by one degree Celsius (the molar heat capacity) or to raise one gram of a substance by one degree Celsius (the specific heat capacity). Heat capacity is related to a substance's ability to retain heat and the rate at which it will heat up or cool. For example, a substance with a low heat capacity, such as iron, will heat and cool quickly, while a substance with a high heat capacity, such as water, heats and cools slowly. This is why on a hot summer day the water in a lake stays cool even though the air above it (which has a low heat capacity) heats quickly, and why the water stays warm at night after the air has cooled.

Water has one of the highest heat capacities of all substances. It takes a great deal of heat energy to change the temperature of water compared to metals. The large amount of water on Earth means that extreme temperature changes are rare on Earth compared to other planets. Were it not for the high heat capacity of water, our bodies (which also contain a large amount of water) would be subject to a great deal of temperature variation.