Thermal capacities: system or process properties?

Abstract

Abstract We discuss the definitions of thermal capacities and make clear that these quantities are system properties. This clarification is pertinent since, in an initial approach to this topic, thermal capacities are defined by resorting to heat, which is not a system property, but a process property. Obtaining a system property from a process property is usually done by restricting its definition to particular processes, which is neither educationally attractive nor necessary. Furthermore, it is shown that dissipative work is as required as heat in defining a system property, but this fact is repeatedly ignored in the literature. For illustrative purposes, the formalism is then applied to a general process carried out by an ideal gas. Beyond scientific aspects, this work has a significant educational nature, as it may help dispel some misunderstandings related to the concepts covered herein.