Know About Open System in Thermodynamics

Dhristi JEE 2022-24

Open System in Thermodynamics

Thermodynamics refers to the study of the transfer of energy that occurs in molecules or collections of molecules. When we are discussing thermodynamics, the particular item or collection of items that we’re interested in is called the system, while everything that's not included in the system we have defined is called the surroundings. 

For instance, if you were heating a pot of water on the stove, the system might include the stove, pot, and water, while the environment would be everything else: the universe, galaxy, planet, country, neighbourhood, house, and rest of the kitchen. The system and therefore the surroundings together structure the universe. Let us define what an open system is.

About Thermodynamics

Thermodynamics deals with concepts such as heat and temperature, as well as the transfer of heat and other forms of energy.

The four laws of thermodynamics, which offer a quantitative description, regulate the behaviour of these values. William Thomson originated the term thermodynamics in 1

It goes through how thermal energy is converted into and out of different forms of energy, as well as how this impacts matter.

Thermal energy is the energy that is derived from heat. Heat is generated by the movement of small particles within an item, and the faster these particles move, the more heat is generated.

Thermodynamics is not concerned with how quickly these energy transformations occur. It is based on the changing states' initial and final states. 

It's also important to remember that thermodynamics is a macroscopic subject. This means it's more interested in the whole system than in the molecular structure of things.

Thermodynamic System

A thermodynamic system is a physical entity with a defined boundary on which we focus our attention. The system border can be real or imagined, and it can be fixed or flexible.

There are three sorts of systems in thermodynamics: open, closed, and isolated.

  • Isolated System - No exchange of energy or mass between an isolated system and its surroundings. The universe is a solitary system. A perfect isolated system is tough to return by, but an insulated drink cooler with a lid is conceptually almost like a real isolated system. The items inside can exchange energy with one another, which is why the drinks get cold, and therefore the ice melts a touch, but they exchange little or no energy with the outside environment.

  • Closed System - Within a closed system, energy is transferred but not mass. Closed systems include refrigerators and piston-cylinder assemblies. example, if we put a very tightly fitting lid on the pot, it would approximate a closed system.

  • Open System - In an open system, both mass and energy can be transmitted. An open system can exchange both matter and energy that is present with its surroundings. Steam turbines and the stovetop example would be an open system because heat and water vapour are often lost to the air. 

Open System in Thermodynamics - Explanation

An open system may be a system that has external interactions. Such interactions can take the shape of data, energy, or material transfers into or out of the system boundary, counting on the discipline which defines the concept.

In contrast to closed systems, the majority of genuine thermodynamic systems are open systems that exchange heat and work with their surroundings. 

As they grow and develop, living systems, for example, are definitely capable of attaining a local reduction in entropy. They construct structures with greater internal energy (i.e., lower entropy) from the nutrients they take. 

The matter is easily exchanged between the open system and its surroundings. This can be described simply by adding or subtracting matter. 

Energy exchange, on the other hand, can be a little more complicated because energy is frequently transmitted in multiple forms and different transformations might occur throughout this process. Heat or another sort of energy is exchanged.

The energy exchange is defined in thermodynamic terms as:

  • Potential Energy

  • Kinetic Energy

  • Thermal energy

Potential energy is stored energy. Kinetic energy is the energy-carrying by an object while moving. However, the energy of a system always exists in one of these three states or in two states at an equivalent time. For example, a stationary object can exchange heat with the encompassing. Then it's both P.E. and thermal energy. Energy is often exchanged or transferred as P.E. or K.E. But sometimes, P.E is often converted into K.E or the other can occur. Thermal energy or heat is additionally exchanged between open systems and their surroundings.

For an example of an open system in thermodynamics, the earth can be recognized as an open system. In this case, the world is the system and space is the surrounding. Sunlight can reach the world’s surface and we can send rockets to space. Sunlight and rockets are often explained as energy and matter, respectively.

Due to the potential of exchanging matter between an open system and surrounding, the interior mass of an open system varies with time. If the matter is added, then an increase in the mass can be found and if the matter is removed, then The first decrease in the mass is found.

The first law of thermodynamics considers the big picture. It discusses the overall amount of energy in the universe and, more importantly, it states that this total amount does not fluctuate. Let’s dig deeper into the First Law of Thermodynamics.

First Law of Thermodynamics For an Open System

The first law of thermodynamics is big: It deals with the entire amount of energy within the universe, and it states that this total amount doesn't change. Put differently, the primary Law of Thermodynamics states that energy can't be created or destroyed. It can only change shape or be transferred from one object to a different one.

This law could seem quite abstract, but if we start to see examples, we’ll find that transfers and transformations of energy happen around us all the time. 

For Example:

Light bulbs convert electricity into light energy (radiant energy).

One ball hits another, transferring K.E. and making the second ball move.

Plants convert the energy of sunlight (radiant energy) into energy stored in organic molecules.

Importantly, none of these transfers is completely efficient. Instead, in each scenario, a number of the starting energy is released as thermal energy. When it's moving from one object to another, thermal energy is named by the more familiar name of warmth. It's obvious that glowing light bulbs generate heat additionally to light, but moving pool balls do too, as do the inefficient energy transfers of plant and animal metabolism. To see why this heat generation is vital, stay tuned for the Second Law of Thermodynamics.

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Difference Between the Open System and Closed System in Thermodynamics

Open System

Closed System

An open system is a type of thermodynamic system where  the energy and matter are often exchanged with its surrounding. 

A closed system is a type of thermodynamic system where only the energy can be exchanged with its surrounding but not matter.

Open system can exchange matter with the surrounding.

Open system cannot exchange matter with the surrounding.

In the case of open systems, the mass of the system will vary with time.

In the case of closed systems, the mass of the system is constant.

Open systems have boundaries that are not closed.

The boundary of a closed system is totally closed.


The interactions between systems and their surroundings can be found everywhere in the environment. Systems can be divided into opened, closed, or isolated systems. The main difference between open and closed systems is that in the case of an open system, matter can be exchanged with the surroundings whereas, in the case of a closed system, matter cannot be exchanged with the surroundings.

FAQs on Know About Open System in Thermodynamics

1. It is Said That in an Open System Work Is Done. How?

In the case of an open system, the transfer of energy takes place in three forms according to the first law of thermodynamics as in the form of work, in the form of heat, or in the form of energy that is associated with the matter. 

The material that is present in the system = Amount of material entering the system - Amount of materials leaving the system.

∆E inside the system = ∆E in - ∆E out

2. Explain through an example, what are the differences between an open system and a closed system in Thermodynamics?

Closed systems are those in which mass remains constant but energy can flow through the system's boundaries, which is why they're also known as control mass systems.

Example: A closed system is a gas-filled container with a movable piston since altering the volume by adjusting the piston causes a change in the temperature of the gas, indicating that thermal energy flowed in the system but the gas's mass remained constant.

Open systems are those in which mass and energy can both flow across the system's boundaries. The control volume is another name for them.

Example: A water heater is an open system since cold water enters the system while hot water exits, implying that energy and mass both move over the system's boundaries (control volume).

3. Are there any limitations of the First Law of Thermodynamics?

According to the First Law of Thermodynamics, heat is a type of energy. As a result, the concept of energy conservation applies to thermodynamic processes. This method does not allow for the creation or destruction of heat energy. It may, however, be transferred from one location to another and transformed into various forms of energy.


When a system goes through a thermodynamic process, it must always keep an exact energy balance, because that's what the law says. The first law, on the other hand, fails to take into account the system's process of change of state feasibility.

4. Who gave the Laws of thermodynamics and what is its purpose?

Both the First and Second Laws of Thermodynamics, which preserve total energy, were established around 1850 by Rudolf Clausius and William Thomson (Kelvin). Originally, the Second Law was based on the notion that heat does not naturally move from a cooler to a hotter body.

The purpose of Thermodynamics is to interplay between heat and other energy sources. It discusses how thermal energy is moved into and out of other energy sources, as well as how it affects matter.

5. What are the different Laws of Thermodynamics?

Three laws govern the thermodynamic systems’ phenomena, they are:

First Law of Thermodynamics

The first law, which is also called the Law of Conservation of Energy, says that energy can't be made or taken away from an isolated system.

Second Law of Thermodynamics

According to the second law of thermodynamics, the entropy of every isolated system always increases.

Third Law of Thermodynamics

According to the third rule of thermodynamics, when the temperature approaches absolute zero, the entropy of a system approaches a constant value.

6. What do you understand about Entropy?

The entropy of a system is a thermodynamic quantity whose value is determined by its physical state or condition. In other terms, it is a thermodynamic function that is used to quantify disorder or randomness.

According to another interpretation of the second law of thermodynamics, a system's total entropy either grows or remains constant; it never decreases. Entropy is zero in a reversible process and grows in an irreversible process.

For instance, the entropy of a solid, in which particles are immobile, is smaller than the entropy of a gas, in which particles fill the container.