A thermodynamic system (such as the air in a balloon) is said to have a certain state specified by the values of its thermodynamic parameters (for example, p, V, n and T). When the values of the parameters change, then we say that the state of the system changes. When a system undergoes a change of thermodynamic state, we say that it has undergone a thermodynamic process . There are four special processes with which you must be familiar. They are listed and defined below.

Isothermal Process

A system is said to undergo an isothermal process when its temperature remains a constant. (The prefix iso- tells us that something is constant.)

Isobaric Process

Recall that a barometer is a device to measure pressure. An isobaric process is therefore one in which the pressure remains constant.

Isovolumetric Process

This is also sometimes called an isochoric process. In such a process, the volume of the system remains constant.

Adiabatic Process

An adiabatic process takes place in such a way that no heat-energy is exchanged between the system and its environment. This can be accomplished by carrying out the process in an insulated container, or it can be approximated by performing the process very quickly, since heat flow is a relatively slow process. (We will not be having much use of adiabatic processes in this course. However, you should be bumping into this kind of process in your study of chemistry or engineering (or more physics!). We therefore include it in this list for completeness.)