|
Heat is a form of energy associated with the random motion of atoms and molecules. In general heat tends to "flow" from a region of high temperature to a region of low temperature. In an isolated system, heat will tend to disperse throughout the entire system until all points equilibrate at the same temperature. |
|
Heat is related to energy in a similar fashion to how work is related to energy. Heat is said to flow from areas of high Temperature to areas of low temperature. Essentially, all objects have a certain amount of energy within them that is related to the random motion of their atoms. This internal energy is directly proportional to the temperature of the object. When two bodies of different temperature come in to thermal contact, they will exchange internal energy until the temperature is equalized. The amount of energy transfered is the amount of heat exchanged. It is a common misconception to confuse heat with internal energy, but there is a difference, and understanding the difference is a necessary part of understanding the [First law of thermodynamics]?. |
|
The amount of heat required to heat a material from an initial temperature, T0, to a final temperature, Tf depends on the the [heat capacity]? of that material according to the relationship: |
Changes of TemperatureThe amount of heat required change the temperature of a material from an initial temperature, T0, to a final temperature, Tf depends on the the [heat capacity]? of that material according to the relationship: |
|
In a sense, the heat capacity is a measure of a material's ability to store heat. |
|
The heat capacity is dependent on both the amount of material that is exchanging heat and its properties. The heat capacity can be broken up in several different ways. First of all, it can be represented as a product of mass and specific heat capacity (more commonly called specific heat): Cp = m cs or the number of moles and the molar heat capacity: Cp = n cmolar Both the molar and specific heat capacities only depend upon the physical properties of the substance being heated, not on any specific properties of the sample. The above definitions of heat capacity only work approximately for solids and liquids, but for gases they don't work at all most of the time. The molar heat capacity can be "patched up" if the changes of temperature occur at either a constant volume or constant pressure. Otherwise, it's generally easiest to use the first law of thermodynamics in combination with an equation relating the internal energy of the gas to its temperature. Changes of StateA boiling pot of water, at atmospheric pressure, will always be at 100oC no matter how much heat is added. The heat in circumstances such as this is said to be "hidden", and thus it is called latent heat (latent is Latin for hidden). Latent heat is the rate of heat per unit mass necessary to change the state of a given substance. Thus: dQ/dm = L (should this be a partial derivative or a full one?) and: Q = ∫(m = Mo, m = M) L dm where Mo is the amount of mass initially in the new phase, and M is the amount of mass that ends up in the new phase. L generally doesn't depend on the amount of mass that changes phase, so the equation can normally be written: Q = L Δm Sometimes L can be time dependednt if pressure and volume are time varying, so that the integral can be handled: Q = ∫L (dm/dt) dt someone check the above, please, to see if the latent heat really depends on where on the (P, V, T) curve the transition is taking place. How Heat Moves |
![[Home]](wikipedia.png)