First law of thermodynamics
From the Simple English Wikipedia, the free encyclopedia that anyone can change
The first law of thermodynamics says that heat transfer is a form of energy transfer and that energy does not vanish (law of conservation of energy).
The most common wording of the first law of thermodynamics is:
| “ | The increase in the internal energy of a thermodynamic system is equal to the amount of heat energy added to the system minus the work done by the system on the surroundings. | ” |
[change] History
James Prescott Joule was the first who found out by experiments that heat and work are convertible.
The first explicit statement of the first law of thermodynamics was given by Rudolf Clausius in 1850: "There is a state function E, called `energy', whose differential equals the work exchanged with the surroundings during an adiabatic process."
[change] Thermodynamics and Engineering
In thermodynamics and engineering, it is natural to think of the system as a heat engine which does work on the surroundings, and to state that the total energy added by heating is equal to the sum of the increase in internal energy plus the work done by the system. Hence δW is the amount of energy lost by the system due to work done by the system on its surroundings. During the portion of the thermodynamic cycle where the engine is doing work, δW is positive, but there will always be a portion of the cycle where δW is negative, e.g., when the working gas is being compressed. When δW represents the work done by the system, the first law is written:
Very occasionally, the sign on the heat may be inverted, so that δQ is the flow of heat out of the system, and δW is the work into the system:
Because of this ambiguity, it is vitally important in any discussion involving the first law to explicitly establish the sign convention in use.
[change] References
- Goldstein, Martin, and Inge F., 1993. The Refrigerator and the Universe. Harvard Univ. Press. A gentle introduction.
