THERMODYNAMIC SYSTEM AND SURROUNDING

When we are discussing thermodynamics, the particular item or collection of items that we’re interested in (which could be something as small as a cell, or as large as an ecosystem) is called the system, while everything that's not included in the system we’ve defined is called the surroundings.

Generalized depiction of the system (a circle), the surroundings (a square surrounding the circle), and the universe (system + surroundFor instance, if you were heating a pot of water on the stove, the system might include the stove, pot, and water, while the surroundings would be everything else: the rest of the kitchen, house, neighborhood, country, planet, galaxy, and universe. The decision of what to define as the system is arbitrary (up to the observer), and depending on what you wanted to study, you could equally well make just the water, or the entire house, part of the system. The system and the surroundings together make up the universe.

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

• An open system can exchange both energy and matter with its surroundings. The stove top example would be an open system, because heat and water vapor can be lost to the air.

• A closed system, on the other hand, can exchange only energy with its surroundings, not matter. If we put a very tightly fitting lid on the pot from the previous example, it would approximate a closed system.

Example of isolated system

• An isolated system is one that cannot exchange either matter or energy with its surroundings. A perfect isolated system is hard to come by, but an insulated drink cooler with a lid is conceptually similar to a true isolated system. The items inside can exchange energy with each other, which is why the drinks get cold and the ice melts a little, but they exchange very little energy (heat) with the outside environment.