# 12: Applications of the Thermodynamic Criteria for Change

- Page ID
- 151738

The equations we derive in Chapters 9 and 10 are the core of chemical thermodynamics. However, we have yet to deal with the effects of changing the concentrations of the substances present in the system. To apply our theory to chemical changes, we must extend our theory so that it can model these effects. In this chapter, we consider some basic applications that do not involve chemical reactions and in which both intermolecular interactions and the effects of mixing can be ignored. In Chapters 13-16, we develop the application of thermodynamic concepts to processes in which a chemical reaction occurs. We do so in two steps. In Chapter 13, we consider an approximation in which the properties of a multi-component system are determined by the effects of mixing pure substances whose molecules neither attract nor repel one another. In Chapter 14, we begin to consider the general case in which intermolecular interactions can be important.

- 12.1: Mechanical Processes
- When we talk about a purely mechanical process, we have in mind a system in which one or more unchanging objects can move relative to some reference frame. Their movements are described completely by Newton’s laws of motion. The essential distinction between a purely mechanical system and a thermodynamic system is that our models for mechanical systems focus on the motions of unchanging objects; our models for thermodynamic systems focus on the internal changes of stationary objects.

- 12.2: The Direction of Spontaneous Heat Transfer
- The idea that thermal energy can be transferred from a warmer body to a colder one, but not in the opposite direction, is a fundamental assumption in our development of the thermodynamic criteria for change. Therefore, if our theory is to be internally consistent, we must be able to deduce this principle from the criteria we have developed.

- 12.3: Phase Changes - the Fusion of Ice
- Let us consider processes in which transfer of heat from the surroundings melts one mole of ice.

- 12.7: Phase Equilibria - Temperature Dependence of the Melting Point
- Analysis of solid–liquid equilibrium parallels that of liquid–vapor equilibrium.