substances have only two types of specific heats. why?
Answers
Specific heat of a subtance is measured experimentally by adding a known heat to the substance and measuring the resulting temperature change. This works well for solids, but not for gases. For gases, the measurement can be affected by many state variables of the system such as temperature, pressure and volume of the system before and after the heat is added.
Therefore, we use two methods to measure the specific heat of gases, which are at constant volume and constant pressure. The value of heat capacity at constant pressure is always greater than that of constant volume since the former also includes the value of heat energy that is used to do work to expand the substance against the constant pressure as its temperature increases.
In addition, the specific heat capacities of gases other than monoatomic gases are not fixed constants, but vary depending on the temperature. These values are expressed at a specific temperature and they will have different specific heat at different temperatures.