Define and differentiate between open and closed systems.

Open systems exchange both energy and matter with their surroundings, while closed systems exchange only energy and not matter.

In more detail, an open system is one that freely allows both energy and matter to be transferred in an out of the system. For example, a pond would be considered an open system because it can gain or lose water (matter) through processes like evaporation or rainfall, and it can also gain or lose energy through sunlight and heat transfer with the surrounding environment. This means that open systems are often subject to changes in their environment, which can affect the system's overall state. To understand more about the basic characteristics of systems in environmental science, see this overview on Introduction to Systems.

On the other hand, a closed system allows the transfer of energy (in the form of heat or work), but not matter. An example of a closed system would be a sealed bottle of water. While the bottle can gain or lose energy (it can be heated or cooled), no matter enters or leaves the system because the bottle is sealed. This means that the total mass of a closed system remains constant. However, the state of the matter within the system can change. For example, the water in the bottle could evaporate into steam or freeze into ice, but it would still remain within the bottle. Understanding how energy interacts in such systems is fundamental and can be further explored in the Laws of Thermodynamics.

It's important to note that these are idealised concepts. In reality, perfectly closed systems rarely exist, as there is often some degree of matter transfer, however small. For example, even a sealed bottle isn't a perfectly closed system on a molecular level, as some molecules can escape or enter through microscopic pores in the material. Similarly, open systems can have limitations on the type and amount of matter and energy that can be transferred, due to physical constraints or regulatory processes.

Understanding the difference between open and closed systems is crucial in environmental systems and societies, as it helps us understand and predict how different systems respond to changes in their environment. For example, the Earth can be considered a closed system in terms of matter (because very little matter enters or leaves the planet), but an open system in terms of energy (because it constantly receives energy from the Sun and radiates energy into space). This has important implications for phenomena like climate change and the carbon cycle. For a deeper insight into how energy is transferred within these systems, the page on Energy Transfers provides detailed information.