First law of Thermodynamics Wiki [Mechanical engineering]

First law of Thermodynamics Wiki

Zeroth law of thermodynamics

states that if two thermodynamic systems are each in thermal equilibrium with a third, then they are in thermal equilibrium with each other.

Two systems are said to be in the relation of thermal equilibrium if they are linked by a wall permeable only to heat, and do not change over time. As a convenience of language, systems are sometimes also said to be in a relation of thermal equilibrium if they are not linked so as to be able to transfer heat to each other, but would not do so if they were connected by a wall permeable only to heat. Thermal equilibrium between two systems is a transitive relation.

The physical meaning of the law was expressed by Maxwell in the words: "All heat is of the same kind". For this reason, another statement of the law is "All diathermal walls are equivalent".

The law is important for the mathematical formulation of thermodynamics, which needs the assertion that the relation of thermal equilibrium is an equivalence relation. This information is needed for a mathematical definition of temperature that will agree with the physical existence of valid thermometers.

Zeroth law as equivalence relation

A system is said to be in thermal equilibrium when it experiences no change in its observable state (i.e. macrostate) over time. The most precise statement of the zeroth law is that thermal equilibrium constitutes an equivalence relation on pairs of thermodynamic systems. In other words, the set of all equilibrated thermodynamic systems may be divided into subsets in which every system belongs to one and only one subset, and is in thermal equilibrium with every other member of that subset, and is not in thermal equilibrium with a member of any other subset. This means that a unique "tag" can be assigned to every system, and if the "tags" of two systems are the same, they are in thermal equilibrium with each other, and if they are not, they are not. Ultimately, this property is used to justify the use of thermodynamic temperature as a tagging system. Thermodynamic temperature provides further properties of thermally equilibrated systems, such as order and continuity with regard to "hotness" or "coldness", but these properties are not implied by the standard statement of the zeroth law.

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FAQ What is the first law of thermodynamics states?

The first law of thermodynamics is the change in internal energy is equal to the heat added minus the work done by the system. First law of thermodynamics states what?

The First Law of Thermodynamics is the Law of Conservation of Energy - in other words, the total amount of energy in a closed system remains constant.