Which concept describes the flow of heat in an isolated system?

The concept that describes the flow of heat in an isolated system is that there is no flow of energy into or out of the system. In an isolated system, by definition, there is complete thermal isolation from the surroundings, meaning that neither heat nor matter can enter or leave the system. This principle aligns with the law of conservation of energy, which states that energy cannot be created or destroyed in an isolated system, only transformed from one form to another.

In such a system, any heat generated internally must remain within the system unless there is a change in state or a transition occurs due to internal processes, but it cannot exchange energy with its environment. Therefore, heat transfer, as traditionally conceptualized (from hot to cold bodies or vice versa), does not occur in an isolated system as there is no external reference point to facilitate that transfer.

For better understanding, heat does not flow from cold to hot, as this would contradict the second law of thermodynamics. Similarly, the idea that heat is continuously lost to the environment applies to non-isolated systems. The concept of heat moving in one direction does not accurately capture the unique property of isolation in which no energy flows take place at all.