What defines a closed system in terms of energy?

A closed system in terms of energy is characterized by the ability to transform energy but not exchange it with the surroundings. This means that while the energy can change forms within the system (for instance, chemical energy can be transformed into thermal energy), no energy is lost or gained from the external environment.

In a closed system, the total amount of energy remains constant, adhering to the law of conservation of energy. This concept is fundamental in many scientific disciplines, including physics and chemistry, as it allows for the study and prediction of energy transformations without the complications introduced by energy transfers with the external surroundings.

The other options describe scenarios that do not align with the definition of a closed system: allowing energy exchange contradicts the closed system principle, stating that a system absorbs energy completely implies potential loss to the surroundings isn't considered, and generating energy continuously without input suggests a violation of fundamental physical laws, particularly the conservation of energy.