The First Law of Thermodynamics
Closed and open systems are considered in thermodynamics. In the former, there is no inflow or outflow of a substance through a boundary. This corresponds to an enclosed space. In the latter, there may be inflow or outflow of a substance through a boundary. The case which has no exchange of a substance or energy between a system and its surroundings is called an isolated system. In an isolated system, after a period of time, the temperature of the system becomes static without temporal change. This is called thermal equilibration, or temperature equilibration. After a period of time of bringing different temperatures into contact with each other, the state reaches thermal equilibration.