# Closed Systems in Thermodynamics and Chemistry In the study of thermodynamics and chemistry, the concept of closed systems emerges as a fundamental pillar for the detailed understanding of energy processes and chemical reactions.

These systems, characterized by their inability to exchange mass with their environment, but allowing the exchange of energy, play an essential role in various scientific disciplines.

This article will delve into the nature and applications of closed systems, exploring their relevance in the formulation of thermodynamic laws, the prediction of chemical reactions, and their impact on engineering and scientific research.

## Definition: What Is a Closed System?

A closed system is a fundamental concept in thermodynamics and physical sciences that describes an environment that does not exchange mass with its surroundings, but does allow the exchange of energy. In this type of system, the total amount of mass remains constant, but energy can be transferred in the form of heat or work.

The first law of thermodynamics states that the internal energy of a closed system remains constant if there is no exchange of energy with its surroundings.

This definition applies to a wide range of disciplines, from physics to chemistry, providing a framework for understanding and analyzing energy processes and reactions.

## Closed Systems in Thermodynamics In the field of thermodynamics, closed systems are an essential tool to analyze the flow of energy and the transformations that occur within a system.

When working with closed systems in thermodynamics, it is possible to study precisely how the internal energy of the system changes due to heat transfer or work done.

This is expressed mathematically by the equation:

ΔU=Q−W

where

• ΔU is the change in internal energy.
• Q is the heat transferred to the system.
• W is the work done by the system.

## Closed Systems in Chemistry In the field of chemistry, closed systems also play a crucial role in the study of chemical reactions.

By considering a closed system containing reactants and products, it is possible to apply the principles of thermodynamics to predict the course of the reaction and understand how energy is redistributed during the process.

The concept of enthalpy (H), which represents the total amount of energy of a system at constant pressure, is particularly relevant in this context. The enthalpy change, ΔH, is related to the amount of heat absorbed or released during a chemical reaction at constant pressure. If ΔH is negative, the reaction is exothermic, releasing heat to the surroundings. On the contrary, if ΔH is positive, the reaction is endothermic, absorbing heat from the surroundings.

The application of closed systems in chemistry allows us to understand not only the direction of a reaction, but also the conditions under which it takes place.

## Examples of Closed Systems

Closed systems are concepts applicable in a variety of disciplines, from physics to biology, and are manifested in everyday situations.

Here, we present illustrative examples of closed systems in different contexts:

• Coffee thermos : A thermos filled with coffee is a closed system in terms of mass transfer, since it does not allow liquid in or out. However, it can exchange heat with the surroundings, keeping the drink warm due to its thermal insulation.
• Refrigerator refrigeration cycle : In a refrigeration system, the refrigerant circulates in a closed loop. Although no refrigerant is lost, the system exchanges heat with its surroundings to cool a specific space.
• Ecosystem in an aquarium : Although the amount of water and organisms remains constant, energy and nutrient exchanges occur with the environment, such as light for photosynthesis and the absorption of nutrients from the water.
• Piston cylinder in a heat engine : In an internal combustion engine, the cylinder with the air-fuel mixture is a closed system during the combustion phase. Although there is no exchange of mass, mechanical work and heat transfer occur.
• Solar System : On an astronomical scale, the solar system can be considered a closed system in terms of mass, since most celestial bodies maintain their orbit without exchanging significant mass. However, energy continually flows from the Sun to the planets.
• Reaction flask in chemistry : A closed flask in a chemical laboratory, used to carry out reactions, is a closed system in terms of the mass of reactants and products, although it can exchange energy in the form of heat with its surroundings.
• Solar water heater : A solar water heater consists of collector tubes filled with a fluid that absorbs solar radiation. Although the fluid can transfer heat to the water through a heat exchanger, the system itself maintains a closed cycle, preventing mass loss.
• Universe : The universe is the only system that can be considered completely closed. Despite the constant interactions and transformations of energy within the universe, the total amount of matter remains constant on astronomical scales.

## Relationship with the Laws of Thermodynamics and Physics

In the study of closed systems, it is worth mentioning the relationship between these systems and the first two laws of thermodynamics. In this context, the law of conservation of mass and Einstein's energy equation are also important.

### First Law of Thermodynamics

According to the first law of thermodynamics, the change in internal energy in closed systems is the algebraic sum of the work done on the system and the heat added to the system. This law establishes a basic principle of energy conservation, providing a basis for analyzing and quantifying energy changes in such systems.

### Second Principle of Thermodynamics

The second law of thermodynamics postulates that the entropy of a closed system tends to increase with the absorption of heat and the dissipation of work. This principle reflects the natural tendency of systems towards states of greater disorder or randomness, basing the concept of irreversibility in many processes.

### Conservation of Dough

In closed systems, the principle of conservation of mass of classical physics also applies, where the mass of the system remains constant.

### Relativistic Physics: Einstein's Equation

In relativistic physics, an additional perspective is introduced: the decrease in the energy content of a system automatically leads to a decrease in the mass of the system, according to Einstein's famous equation E=mc².

This aspect reveals the interconnection between mass and energy, providing deeper insight into environments where speeds close to the speed of light are relevant.

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Published: February 26, 2021
Last review: November 15, 2023