Define energy and apply conservation of energy to closed systems.

The law of conservation of energy is an important law of physics. Basically, it says that while energy can turn from one kind into another, the total amount of energy doesn't change. This law applies only to closed systems, meaning systems that can't exchange energy with their environment.

Explanation:

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before, trains worked using the steam engine. thus, it uses heat so it is crucial to apply heat balance. the steam engine absorbs energy during the stage of boiling water. so, this is the endothermic reaction. when the steam is used to work the piston, it has to release this energy through running the train. the excess energy is released as an exhaust to the chimney. this is the exothermic process because it releases energy to the surroundings.