Difference Between Open and Closed System

Main Difference – Open vs Closed System

Thermodynamics is a branch of physics which explains the energy transfer between objects and surrounding. Terms in thermodynamic can also be used to understand chemical behavior of chemical species. System and surrounding are two basic terms used in thermodynamics. A system is a part of the universe which is being studied and surrounding is the rest of the universe other than that particular system. The margin of the system which separates it from the surrounding is called boundary. Systems can exist in three ways as open systems, closed systems, and isolated systems. The main difference between open and closed system is that in an open system, matter can be exchanged with the surrounding whereas, in a closed system, matter cannot be exchanged with the surrounding.

Key Areas Covered

1. What is an Open System
      – Definition, Characteristics
2. What is a Closed System
      – Definition, Characteristics
3. What is the difference between Open and Closed Systems
      – Comparison of Key Differences

Key Terms: Energy, Kinetic Energy System, Matter, Potential Energy, Surrounding, Thermodynamics

What is an Open System

An open system can be defined as a system which can exchange both matter and energy with the surrounding. For example, the earth can be recognized as an open system. In this case, the earth is the system, and space is the surrounding. Sunlight can reach the earth surface and we can send rockets to space. Sunlight and rocket can be explained as energy and matter, respectively.

Exchange of matter between the open system and the surrounding occurs easily. This can also be easily explained by adding matter or removing matter. But energy exchange is a bit more complicated because energy can be exchanged in different forms and different conversions may occur during this exchange. Energy is exchanged as heat or any other form.

In thermodynamic terms, energy exchange is characterized by potential energy, kinetic energy, and thermal energy. Potential energy is the 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 the same time. For example, a stationary object can exchange heat with the surrounding. Then it has both potential energy and thermal energy. Energy can be exchanged or transferred as potential energy or kinetic energy. But sometimes, potential energy can be converted into kinetic energy or the opposite can occur. Thermal energy or heat is also exchanged between open systems and their surroundings.

Due to the capability of exchanging matter between open system and surrounding, the internal mass of an open system varies with time. If matter is added, the mass will increase and if matter is removed, the mass will decrease.  

Figure 1: Since the mug is not covered, both energy and matter can be exchanged with the surrounding. Thus, this is an open system.

What is a Closed System

A closed system is a system where only energy can be exchanged but not matter. Matter cannot be exchanged in a closed system because matter contains particles which cannot cross the boundary of the system. But energy is passed through this boundary as photons because energy is not particulate. Therefore, in a closed system, the mass remains constant because the matter cannot be removed or added. But energy can be transferred mostly as heat or thermal energy.

For example, if a warm cup of water is covered by placing a lid on the top of the cup, then steam cannot escape the system because of the lid. The gas molecules in the air also cannot enter the cup because of the lid. So, there is no exchange of matter. But if we touch the lid after some time, we can feel that it is warm. The cup also will feel warm; this indicates that energy is coming outside as thermal energy.  If this system is kept at a normal temperature for a long time, it can be observed that the cup, lid or water is no longer warm. This is because the system has shared heat energy with the surrounding until the temperature of the system becomes equal to the temperature of the surrounding. This is called an equilibrium.

Figure 2: The covered pot is an example of a closed system since it cannot exchange matter with the surrounding because of the lid.

Difference Between Open and Closed Systems

Definition

Open System: An open system is a thermodynamic system where energy and matter can be exchanged with its surrounding.

Closed System: A closed system is a thermodynamic system where energy can be exchanged with its surrounding but not matter.

Exchange of Matter

Open System: Open systems can exchange matter with the surrounding.

Closed System: Closed systems cannot exchange matter with the surrounding.

Internal Mass

Open System: The mass of the system will vary with time in open systems.

Closed System: In closed systems, the mass of the system is constant.

Boundary of the System

Open System: Open systems have boundaries which are not closed.

Closed System: The boundary of a closed system is completely closed.

Conclusion

Everywhere in the environment, there are interactions between systems and their surroundings. Systems can be either opened, closed or isolated. The main difference between open and closed system is that, in open system, matter can be exchanged with the surrounding whereas, in a closed system, matter cannot be exchanged with the surrounding.

References:

1.”A System and Its Surroundings.” Chemistry LibreTexts. Libretexts, 21 July 2016. Web. Available here. 16 June 2017.
2.”Open, Closed and Isolated Systems in Physical Chemistry.” Foundations of Physical Science. N.p., n.d. Web. Available here. 16 June 2017. 

Image Courtesy:

1. “345707” (Public Domain) via Pixabay
2. “coffee steam 2” by waferboard (CC BY 2.0) via Flickr