Some key basic concepts on thermodynamics

Thermodynamicists tend to use words for technical aspects of this subject. This words are used for other subjects but with some restrictions or further details that help to describe what they are talking about.

Not knowing the meaaning of these concepts would be as trying to comunicate with someone from another country using a different language. This case is not that extreme but difficulties could arise and the worst, you will wste time.

Then, consider the following concepts, presented in a colloquial manner.

Frst, body and system come as words referring to physical things that may be the same for certain circumstances. Perhaps, a difference we can make a first difference between body and system: a system may involve more than one body. In a body and in a system physical and chemical changes, that can be measured, may occur. Next, these measurements, also understood as data, help to describe, in detail, the body or system, or we should say characterized it. Also, the features or parameters to be measured in a body or system may be important due to its changes in time or relation to other features are known as properties.

On the other hand, a system has another feature: it denotes a region or space which is restricted by boundaries with different features such as: thermal conductivity, porosity, etcetera. Measurements of the properties of the system allow to define the system in a given set of conditions, which is called a state. Those properties measured to define the state are also called variables of state. 

From the mathematical point of view, there are independent and dependent variables. Next, state properties can be expressed as independent variables.

Main components of a function.

On thermodynamics, it is known, empirically, that in order to estimate the intensive variables of a system, only two intensive variables need to be known. An intensive variable is one that does not depend on the amount of matter in the system. If the value of the variable is proportional to the quantity of matter, then it would be an extensive variable.

The equations inoliving independent and dependent variables of state are called state equations. 

A thermodynamical process implies changes in time of one or more properties. these changes in time can be referred as state changes as well.

Two types of systems can be found. The first ones are closed systems in which mass entrance or leaving is not allowed or never happens. If mass enters or leaves the system, then we would say that the system is open. Similarly, an adiabatic system is a closed system too since no heat is exchanged with the surroundings.

Thermal equilibrium would mean that state variables remain constant boundaries are allowed to change.

Any question? Write in the comments and I shall try to help.

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Ildebrando.