Thermodynamics Basics

Thermodynamics also referred to as heat theory, is a sub-area of classical physics. It is concerned with the possibility of doing work by redistributing energy between its various manifestations. The basics of thermodynamics were developed from the study of the volume, pressure and temperature relationships in steam engines.

A distinction is made between open, closed and closed (isolated) thermodynamic systems. In the case of an open system, in contrast to the closed system, matter flows over the system boundary, closed systems are also energy-tight. According to the energy conservation law, the sum of all forms of energy (thermal, chemical, spring tension, magnetization, etc.) remains constant.

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Thermodynamics relates the process variables heat and work at the system boundary to the state variables that describe the state of the system.

A distinction is made between intensive state variables (for example temperature T, pressure p, concentration n, and chemical potential μ) and extensive state variables (for example internal energy U, entropy S, volume V and particle number N).

On the basis of four fundamental principles as well as material-specific, empirical equations of state between the state variables by establishing equilibrium conditions, thermodynamics allows statements to be made about which changes to a system are possible (e.g. which chemical reactions or phase transitions can take place, however not how) and which values ​​of the intensive state variables are required for this.

It is used to calculate released heat energy, pressure, temperature or volume changes, and is therefore of great importance for understanding and planning processes in chemical plants, for heat engines, and in heating and air conditioning technology.

However, thermodynamics makes no statements about how fast the processes run (kinetics) so that efforts have been made to replace the term thermodynamics with thermostatics.

Through statistical mechanics according to James Clerk Maxwell and Ludwig Boltzmann, many aspects of thermodynamics can be confirmed using microscopic theories. In its entire presentation, however, it still retains the excellent status of an independent physical theory.


However, their applicability must be restricted to suitable systems, namely those that are made up of a sufficient number of individual systems, i.e. mostly particles.

Thermodynamics Laws

Open system

There are energy and material transfer between the system and the environment.

Closed system

There is only energy transfer between the system and the environment, there is no material transfer.

Isolated system

There is neither energy transfer nor material transfer between the system and the environment.