System and Surroundings
This video presents the same text shown beside it, spoken and on screen. It adds nothing the text does not say.
State
The system is the matter undergoing a studied change; the surroundings are everything else able to exchange heat with it.
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In a calorimetry experiment, the reacting substances are the system, while the surrounding solution and calorimeter body count as the surroundings.
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The system/surroundings boundary is a choice the observer draws for the analysis, not a physical wall built into the apparatus.