Fundamentals of Chemical Engineering Thermodynamics

Chapter 3. Energy and the First Law

A classical mechanical system is characterized by a set of mechanical state variables: velocity, elevation in a gravitational field, electrical charges, and so forth. If these variables are given and the external fields are known, the system is fully specified and its behavior at any instant of time, past or future, can be calculated. Thermodynamic systems are characterized by an additional state variable: temperature. Unlike mechanical variables, which describe external interactions, temperature characterizes the internal state of macroscopic matter. Temperature is a measure of the energy stored inside matter in various forms, which we collectively call internal energy. Temperature gives rise to another type ...