Thermal equilibrium - Energy Education
Heat is the flow of energy from a high temperature to a low temperature. When these temperatures balance out, heat stops flowing, then the system (or set of systems) is said to be in thermal equilibrium. Thermal equilibrium also implies that there's no matter flowing into or out of the system.[1] The zeroth law of thermodynamics uses thermal equilibrium to define how two different systems can be said to be at the same temperature. For example, when molten rock comes up from a volcano, it will give off heat to the atmosphere until the rock and the atmosphere are at the same temperature. Even though the two systems (rock and air) are very different, thermal equilibrium allows a definition of temperature for both. All systems tend towards thermal equilibrium over time—and some systems will take a lot longer than others. Knowing that interacting systems will tend towards the same temperature allows for important applications in all areas of science. For example, the specific heat capacity
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