14. Heat capacity

Now let's find out the physical meaning of \(c\). If the body mass is equal to one and the temperature changes by one unit, then according to (1-19, \(\Delta Q = cm\Delta t \)) the value of \(c\) is a number which is equal to the quantity of heat. Then the constant \(c\) is numerically equal to the quantity of heat that needs to be transferred to the one unit of mass of the substance in order to change its temperature by one degree. This value is called the Specific heat capacity of the substance. It characterizes the thermal properties of the substance. The quantity of heat needed to increase the temperature by one degree in a body of any mass is called the Heat capacity of the body. The heat capacity of one mole of a substance is called molar heat capacity.

In the experiments on observation of heat exchange between bodies, as we have seen, the quantity of heat is conserved. On the basis from this fact there was a theory of caloric, in which heat was considered as an undestroyable, weightless liquid. From the point of view of caloric theory, the heat capacity is the same as the normal container capacity. Just as at transfer in a container of some quantity of a liquid its level in a container raises the more, than less its cross-section (its capacity), transfer to a body the given quantity of heat the more will increase its temperature, than less heat capacity of a body.

To measure the quantity of heat transferred, a special unit, calorie, was introduced. One calorie is the quantity of heat that you need to transfer to 1 gram of water in order to increase its temperature by \(1^0 \, C\). That is why the specific heat capacity of water by definition was equal to \(1 \, \frac{cal}{gram \times degree} \).

Subsequently (see the following paragraph) it was proved that the quantity of heat is conserved only under certain conditions. The discovery of this fact led to the death of caloric theory. No undestroyable thermal liquid exists. But the terminology related to heat processes, which was created during the reign of the caloric theory, has remained.