Ever wonder why water is such a good coolant? Why it has such a high capacity to absorb heat? It is because of a property called specific heat—and water has one of the highest of any common substance. And what is specific heat? It is the amount of energy required to raise a gram of a substance’s temperature by exactly one degree Celsius.
Specific heat was discovered through the work of a Scottish chemist named Joseph Black (1728-1799). It can be calculated by manipulating the following equation: Q=mcDT.
In this equation:
- “Q” is energy (measured in joules or calories)
- “c” is specific heat (joules or calories/gram)
- “m” is the mass (in grams)
- “DT” is the change in temperature (in Celsius).
The specific heat for water is one calorie per gram. In other words, it takes one calorie (or 4.186 joules/gram of energy) to raise a gram of water by exactly one degree Celsius.
Knowing this fact enables experiments that can determine the specific heat for a variety of substances. For example, immerse a known mass of heated aluminum into a known mass of cool water and the heat transferred from the aluminum will raise the water’s temperature. The specific heat of aluminum can then be deduced by noting the change in both the aluminum’s and the water’s temperature.
Specific heat is not to be confused for a similar property called heat capacity. Heat capacity is dependent on the amount of the substance being heated. For example, a bathtub full of water has a higher heat capacity than a glass of water because there is more water to heat. But they both still have the same specific heat.
- So why do different substances have different specific heats? It depends how easy it is to get their molecules to move. Heat is energy—and energy is motion. When energy is added to a substance, its molecules move faster and we feel the effect as heat.
- So why does water absorb so much heat? This is because of water’s hydrogen bonds. They are very strong, and it takes a large amount of energy to get the hydrogen bonds to break free in order to make the water molecules to move faster.
Heat a copper pot full of water and you will note that the pot heats up faster than the water by just touching the handle. This is because water has a higher specific heat than copper. Another example of specific heat can be found by going to the beach. In the daytime, the beach will heat up faster than the water. This is because land has a lower heat capacity than water. And it is these two battling temperature differences that create a sea breeze.