Closed System: GCSE Physics Definition

What is a closed system?

In GCSE Physics, a closed system is defined as one in which the total energy does not change. Due to energy conservation, the total amount of energy within a closed system must remain constant.

A thermodynamic system can be isolated, closed, or open.  A closed system can exchange energy but not matter to or from its surroundings. Most energy transfer scenarios are modelled in a closed system. An open system allows the exchange of energy and matter to or from its surroundings. In contrast, an isolated system does not allow the transfer of energy to or from its surroundings.

An example of a closed system is a pot of boiling water that is covered by a lid. Heat energy is transferred to the pot and the water, turning the liquid water into gaseous steam. Since the lid prevents the gas molecules from leaving the pot, energy is exchanged, but matter is not.

Another example of a closed system, which is almost an isolated system, is a sealed thermos containing water and ice cubes. Heat energy is transferred to the ice cubes by the water, causing the ice to slowly melt from a solid to a liquid state. A thermos is designed to limit the exchange of energy between the contents and the surroundings, meaning neither energy nor matter is exchanged. However, it is impossible to prevent energy exchanges entirely, which is why it is almost an isolated system.

Closed system revision resources to ace your exams

Understanding the concept of a closed energy system is found only in some GCSE Physics and Combined Science courses. Exam boards are very specific about the energy stores and transfer as well as the system's terminology and when it is used, so make sure you select the right course. Once you are ready to test your knowledge you can use our specific exam practice questions on energy, such as the questions for AQA GCSE Physics on Energy Changes in a System. If you are ready for some general exam revision then you can use the past paper section, for example, the OCR GCSE Physics past papers. 

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