Heat Capacity
Heat capacity is the quantity of heat energy required to raise the temperature of a substance by 1°C. It is a measure of how well a substance stores heat. Numerically it is represented by the mass of a substance multiplied by that substance's specific heat. Historically heat energy has been defined in units of calories. One calorie is the quantity of heat energy required to raise the temperature of 1g of water from 14.5 to 15.5°C. This means that the specific heat of water is 1.0 cal g-1 °C-1 .
According to the second law of thermodynamics, heat flows from a warm body, one with a higher relative temperature, to a cooler body, one with a lower temperature. Heat flows between the two bodies until they reach the same temperature. The quantity of heat energy required to change the temperature of a substance is dependent upon how much the temperature is to be changed, the mass of substance undergoing the change and the type of substance it is composed of. Heat capacity, being the quantity of heat energy required to raise the temperature of a substance by 1°C, is clearly dependent upon the amount of substance undergoing the temperature change. The specific heat required to calculate the heat capacity is independent of the amount of substance by definition.
Another way to think about heat capacity is that it is equal to the heat energy added to the body, divided by the change in temperature. It is easier to think of heat capacity in this way when considering a substance's ability to retain heat. Substances with large heat capacities, like water, hold heat very efficiently. Other substances, such as lead, do not store heat well and therefore their temperature will rise significantly for a given amount of heat energy added.
An additional idea connected with heat capacity is that of the law of conservation of energy that states that in interactions among objects of substances, the total energy remains constant. This means that energy lost by one object must be gained by another object. This law plays an important role in determining the heat capacity of a substance. Since the total heat energy lost by one substance must be equal to that gained by another, one can easily determine the specific heats of substances experimentally. Once the specific heats are known, these values can be multiplied by each substance's mass to obtain the individual heat capacities.
This is the complete article, containing 403 words
(approx. 1 page at 300 words per page).
