Читать книгу Geochemistry - William M. White - Страница 51

It is a matter of everyday experience that the addition of heat to a body will raise its temperature. We also know that if we bring two bodies in contact, they will eventually reach the same temperature. In that state, the bodies are said to be in thermal equilibrium. However, thermal energy will not necessarily be partitioned equally between the two bodies. It would require half again as much heat to increase the temperature of 1 g of quartz by 1°C as it would to increase the temperature of 1 g of iron metal by 1°C. (We saw that temperature is a measure of the energy per degree of freedom. It would appear then that quartz and iron have different degrees of freedom per gram, something we will explore below.) Heat capacity is the amount of heat (in joules or calories) required to raise the temperature of a given amount (usually a mole) of a substance by 1 K. Mathematically, we would say:

(2.66)

However, the heat capacity of a substance will depend on whether heat is added at constant volume or constant pressure, because some of the heat will be consumed as work if the volume changes. Thus, a substance will have two values of heat capacity: one for constant volume and one for constant pressure.