other with respect to the various extensive quantities. If we have a thermodynamic system in equilibrium in which we relax some of its constraints, it will move to a new equilibrium state. The thermodynamic parameters may now be thought of as variables and the state may be thought of as a particular point in a space of thermodynamic parameters. The change in the state of the system can be seen as a path in this state space. This change is called a thermodynamic process. Thermodynamic equations are now used to express the relationships between the state parameters at these different equilibrium state. The concept which governs the path that a thermodynamic system traces in state space as it goes from one equilibrium state to another is that of entropy. The entropy is first viewed as an extensive function of all of the extensive thermodynamic parameters. If we have a thermodynamic system in equilibrium, and we release some of the extensive constraints on the system, there are many equilibrium states that it could move to consistent with the conservation of energy, volume, etc. The second law of thermodynamics specifies that the equilibrium state that it moves to is in fact the one with the greatest entropy. Once we know the entropy as a function of the extensive variables of the system, we will be able to predict the final equilibrium state. Notation Some of the most common thermodynamic quantities are: The conjugate variable pairs are the fundamental state variables used to formulate the thermodynamic functions. The most important thermodynamic potentials are the following functions: Thermodynamic systems are typically affected by the following types of system interactions. The types under consideration are used to classify systems as open systems, closed systems, and isolated systems. Common material properties determined from the thermodynamic functions are the following: The following constants are constants that occur in many relationships due to the application of a standard system of units. Laws of thermodynamics The behavior of a thermodynamic system is summarized in the laws of Thermodynamics, which concisely are: Zeroth law of thermodynamics If A, B, C are thermodynamic systems such that A is in thermal equilibrium with B and B is in thermal equilibrium with C, then A is in thermal equilibrium with C. The zeroth law is of importance in thermometry, because it implies the existence of temperature scales. In practice, C is a thermometer,