Introduction

Thermodynamics is the science that deals with the transformation of energy from one form to another.

Treatment of this subject requires a number of definitions:

• A system is the part of the universe of a process under study.

• A property is any observable characteristic of a system. Temperature, pressure, volume, and entropy are all properties.

• An extensive property is one that depends on a system's mass or size. Volume, internal energy, and entropy are extensive properties.

• An intensive property does not depend on the system mass or size. Pressure, temperature, and molal volume are intensive properties.

• The state of a system refers to and is determined by its properties at equilibrium.

• A process is a change of state determined by a change in properties. If a system's temperature changes, the increase or decrease in temperature is the process.

• A process is reversible if both the system and the surrounding can be restored to their initial state at the end of the process.

To explore the topic of energy, we need a definition of temperature and heat. Any pair of systems without an extraordinary barrier between them will generally affect each other. If the effect involves no exchange in mass across the systems' boundaries, the pair approaches a limiting condition called equality of temperature.

The definition of temperature, in turn, leads to the zeroth law of thermodynamics: If two systems are each equal in temperature to a third system (the third system is...