Heat Capacity:
The heat capacity of an
object is the ratio of the amount of heat transferred to an object to
the rise in temperature of an object. If you know how much heat
energy you have transferred to an object in joules, and the heat
capacity (or its specific heat), you can predict how much
temperature change the object will undergo. This is expressed
as:
Water has a very high specific heat, which is fortunate for us. Because water's heat capacity is large, it doesn't change temperature much upon absorbing large amounts of heat energy from the sun when compared to the temperature change predicted for air. By the way, the "p" in c_p stands for constant pressure, meaning that value is good if the heat energy is absorbed by the object at constant pressure.
Specific heat values for common substances are listed below. Note that the specific heat of water is more than 4 times that of an equal quantity (by mass) of air {realize, of course, that these are not equal volumes of water and air}.
|
|
Specific heat capacity (kJ / (kg x degree K) |
|
Copper |
0.39 |
|
Glass |
0.84 |
|
Human body (average) |
3.5 |
|
Ice (water @ -5 degrees C) |
2.1 |
|
Wood |
1.8 |
|
Water |
4.2 |
|
Air (at 100 degrees C) |
1.0 |
|
Steam (at 110 degrees C) |
2.0 |
If we transfer enough heat energy into 1kg of air (which occupies about 1 cubic meter of volume) we can raise its temperature 1 degree C (or K, same difference). If we turn around and transfer that same amount of heat energy into 1kg of water, we will raise its temperature about 1/4 degree C. Thus we have stored the same amount of heat (in considerably less volume, about 1/1000 the volume of 1kg of air) with 1/4 degree temperature change. Clearly the oceans are a great place to store heat energy in the form of internal energy increases!
A substance can also undergo a phase change whenever heat is enetering or leaving the substance. During this phase change, all the enrgy goes into either melting the substance (or freezing if heat is leaving) or vaporizing (or condensing if heat ios leaving) the substance. The amount of mass that changes pahse depends upon the amount of heat added (Q).
Q=mL
L is called the Latent Heat of Vaporization or Latent heat of fusion depending upon whether the subatcnce is melting or vaporizing.