Physics is a very broad science that encompasses a wide variety of branches that are responsible for studying many of the phenomena that occur in materials, whether physical or chemical. One of these divisions is thermodynamics , which is responsible for analyzing and studying the different relationships that exist between heat and other types of sources that produce energy .


What is thermodynamics?

Thermodynamics is a branch of the area of ​​science whose function is the study of the effects produced by changes in temperature , pressure and volume of a material or liquid at the macroscopic level .

  • Definition
  • Characteristics of thermodynamics
  • What is thermodynamics for
  • Types
  • How it is calculated
  • Formula
  • Units
  • Negative and positive enthalpy
  • How it differs from entropy
  • Importance of thermodynamics
  • Examples


To understand the definition of thermodynamics, it is necessary to know what thermal energy is . This type of energy is that contained in a substance determined by the degree of heat it presents, this can also be said as the energy possessed by all molecules that are in motion. Thermodynamics is then a branch of science whose function is to be able to measure that thermal energy, which is generated by atoms or molecules that interact with each other.


It is based on various laws. The first is known as the principle of conservation of energy and it says that when a system performs a heat exchange with another, the energy inside it is transformed. The second law regulates the direction in which all thermodynamic processes occur and establishes that they cannot occur in the opposite direction. The third law indicates that a thermal mark of zero cannot be obtained by physical procedures.

Characteristics of thermodynamics

Among its main characteristics, the following should be mentioned:

  • The word is composed of the root ” thermos ” which means heat and ” dynamos ” which refers to movement.
  • He uses the scientific method and deductive reasoning to be able to carry out his studies.
  • Take into account the temperature , pressure, and chemical characteristics of the element under study.
  • It began as a formal science thanks to Otto von Guericke in 1650.
  • It uses as a base everything that exists as long as it has a relationship with the passage of energy .

What is thermodynamics for

This science is used to carry out studies and classify the different interactions that can occur between systems that are considered as thermodynamic . Through it, the internal energy of a system as well as its heat potentials can be expressed, which are useful to understand the way in which the temperature balance is achieved , the spontaneous processes and the different types of energy exchange. between those systems and their environment.


There are three different types or systems in thermodynamics, the open, isolated and closed.

  • Open system : in it, exchanges of energy and matter with the environment can take place.
  • Closed system : it only exchanges energy with the environment without touching matter.
  • Isolated system: this system means that neither energy nor matter can be exchanged with the environment.

How it is calculated

Thermodynamics can be calculated when a series of studies are carried out to establish the interaction that exists between heat and energy , the states of equilibrium and the internal energy of a given system.


The way in which it can be calculated is by using the general equation of the conservation of energy but applied to thermodynamics, this formula would then be as follows:

Where U refers to the internal energy, Q to the amount of heat that the system contributes and W to the work that the system does and does.


The units used to measure thermodynamics are shown in the following table:

Physical magnitude Symbol SI unit
job  W J
internal energy OR J
hot Q J
entropy S J K-1
thermodynamic temperature T K
Celsius temperature t or C
ratio Cp / Cv g 1 g 1
heat capacity C JK -1

Negative and positive enthalpy

Enthalpy is understood to be the amount of energy that can be found within a thermodynamic system when it constantly exchanges a series of pressure conditions with the environment . It can also be said that it is the amount of energy that is absorbed or released into the environment through processes that do not change the pressure.

There are several types of enthalpy, one of them is the formation one which represents the amount of heat that can be absorbed or discharged at the moment in which a compound mole is formed, this type of enthalpy can become negative when it comes from a type of reaction that releases heat ( exothermic ) or can be positive when it instead absorbs heat ( endothermic ).

How it differs from entropy

Two of the relationships in thermodynamics are entropy and enthalpy . The first one is the degree of disorder that can be found in a system and enthalpy is the total amount of energy that can be found within a certain system, in other words, the amount of energy that that system possesses. Although they are different concepts, the two are closely linked with thermodynamics.

Importance of thermodynamics

Thermodynamics is an important science because its studies are related to industrial engineering since all industrial processes of material transformation need it to achieve a suitable product in the end. Many processes that are generated within the field of industry depend on thermodynamics as well as various types of natural reactions including, for example, the processes that occur in kitchen appliances . It is important because of use depend on air conditioning systems, heat engines, combustion in aircraft and marine engines, evaporators and compressors.


  • Enthalpy of formation of water : The enthalpy of water when in a liquid state is calculated as 32 ° F.
  • Enthalpy of combustion of methane : its enthalpy is −882.0 kJ / mol.
  • Enthalpy combustion of the butane : standard enthalpy of combustion of butane is -2878.6 kJ / mol.

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