Meaning of Thermodynamics

What is Thermodynamics:

Thermodynamics is the branch of physics that studies the relationship between heat, applied force (also known as work), and energy transfer.

The word thermodynamics comes from the Greek roots θερμο- (thermo-) meaning ‘heat’, and δυναμικός (dynamikós)which in turn derives from δύναμις (dynamis)which means ‘strength’ or ‘power’.

Thermodynamic processes are determined by three basic laws.

  • The first law allows us to understand how energy is conserved.
  • The second law is used to know the necessary conditions for the transfer of energy to occur.
  • The third law serves to know the behavior of systems in equilibrium.

Understanding thermodynamic processes is important in areas such as industrial engineering where large amounts of energy need to be used to run multiple machines.

The laws of thermodynamics also provide an understanding of how systems work in areas such as biochemistry, cosmology, and genetics.

Laws of thermodynamics

There are three laws in thermodynamics that explain how heat and energy work and are transferred. Next, we explain them in detail.

First Law of Thermodynamics

The first law deals with the conservation of energy: energy can neither be created nor destroyed, it can only be transformed. For example:

  1. Solar energy is transformed into electrical energy for a service station.
  2. That electrical energy can be used to charge the battery of the electric car.
  3. The electric car is capable of converting stored energy into displacement.
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Energy, therefore, is always in motion.

The simplified formula would be the following:


Second law of thermodynamics

The Second Law of Thermodynamics allows us to determine two things:

  • The direction in which energy transfer occurs.
  • The conditions that are necessary for the process to be reversed.

From this we learn that there are reversible and irreversible processes.

For example, table salt mixes with water spontaneously through a process called dilution. This process releases heat.

In order to reverse this process and re-form salt crystals, heat must be applied, which allows the water to evaporate and separate it from the salt. The system absorbs heat.

The simplified formula would be the following:


Third law of thermodynamics

The third law of thermodynamics combines the previous two laws and applies them to systems in absolute equilibrium. In this state there is a minimum energy exchange and a maximum degree of disorder (or entropy).

The third law is applied to closed systems. These types of systems are only observed in theoretical physics and chemistry.

The simplified formula would be this:


See also Physics.

Types of systems in thermodynamics

To understand the laws of thermodynamics, it is first important to know the types of systems that exist and their behavior.

Everything around us is made up of systems, and most of the systems we know of exchange energy. Systems are classified into three types: open, closed and isolated.

  • Open Systems: they exchange energy and matter with the outside (for example, a bonfire).
  • Closed systems: they exchange only energy with the outside (for example, a mobile phone).
  • Isolated systems: they do not exchange matter or energy (they are only theoretical).
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While the first and second laws of thermodynamics apply to open and closed systems, the third law applies to isolated systems.

state of a system

There are two fundamental states in which systems (regardless of their type) can be found.

  • active systems: If there is an exchange of energy, the system is said to be active.
  • Systems at rest or equilibrium: If there is no exchange of energy, the system is considered to be at rest or in equilibrium.

Heat and heat transfer in thermodynamics

According to physics, heat is the flow of energy that exists when two systems of different temperatures come into contact. Thermal equilibrium is reached when all the systems involved reach the same temperature.

In thermodynamic systems if two of them are in equilibrium with a third system, then they are also in equilibrium with each other. Therefore, when equilibrium is reached, the temperature is a constant.


See also Branches of physics.