1. | The heat absorbed or evolved in any chemical reaction is a fixed quantity and is independent of the path of the reaction or the number of steps taken to obtain the reaction [Hess’s Law]. | Hess [1840] |
2. | Energy can be neither created nor destroyed. | Mayer [1841] |
3. | The mechanical power exerted in turning a magneto-electric machine is converted into the heat evolved by the passage of the currents of induction through its coils; and, on the other hand, that the motive power of the electro-magnetic engine is obtained at the expense of the heat due to the chemical reactions of the battery by which it is worked. | Joule [1843] |
4. | Vital heat is the product of mechanical forces within the organism; all heat is related to ordinary forces; force itself can never be destroyed. | Helmholtz [1847] |
5. | There is a state function E, called ‘energy’, whose differential equals the work exchanged with the surroundings during an adiabatic process. | Clausius [1850] |
6. | All different kinds of physical energy in the universe are mutually convertible. | Rankine [1853] |
7. | The quantity of force which can be brought into action in the whole of Nature is unchangeable, and can neither be increased nor diminished. | Helmholtz [1863] |
8. | The energy of the world is constant. | Clausius [1865] |
9. | The principle of the conservation of energy applied to phenomena involving the production or absorption of heat. | Planck [1897] |
10. | It is in no way possible, either by mechanical, thermal, chemical, or other devices, to obtain perpetual motion, i.e. it is impossible to construct an engine which will work in a cycle and produce continuous work, or kinetic energy, from nothing. | Planck [1897] |
11. |
The relativity principle, in association with Maxwell’s fundamental equations, requires that the mass be a direct measure of the energy contained in a body; light carries mass with it. [E/m = constant = c2] |
Einstein [1905] |
12. | The variation in energy of a system during any transformation is equal to the amount of energy that the system receives from its environment. | Fermi [1936] |
13. | If any system is carried through a cycle, the end state being precisely the same as the initial state, then the summation of the work delivered to the surroundings is proportional to the summation of the heat taken from the surroundings. | Keenan [1941] |
14. | The change in the internal energy dE, an exact differential, within a bounded region of space is found as a matter of experiment to be equal to the quantity of heat absorbed DQ, an inexact differential, and the amount of work done DW, an inexact differential, by the system. | Koltz [1950] |
15. | dE = DQ - DW | Koltz [1950] |
16. | The internal energy of a system is a single-valued function of its state and varies only under the influence of external actions. | Bazarov [1964] |
17. | Etotal = constant | Bent [1965] |
18. | [Etotal]Final State = [Etotal]Initial State | Bent [1965] |
19. | The total energy of the system plus the surroundings must remain constant. | Lehninger [1971] |
20. | If the state of an otherwise isolated system is changed by the performance of work, the amount of work needed depends solely on the change effected and not on the means by which the work is performed nor on the intermediate stages though which the system passes between its initial and final states. | Adkins [1983] |
21. | An extension of the principle of conservation of energy to include systems in which there is a flow of heat. | Adkins [1983] |
20. | Energy is a conserved property. It can be neither created or destroyed; only its form can be altered from one form of energy to another. | Black & Hartley [1996] |
21. | When a system undergoes a transformation of state, the algebraic sum of the different energy changes, heat exchanged, work done, etc., is independent of the manner of the transformation. It depends only on the initial and final states of the transformation. | Prigogine & Kondepudi [1998] |
26. | When any closed system (control mass) is altered adiabatically, the net work associated with the change of the state is the same for all processes between two given equilibrium states. | Wark & Richards [1999] |
27. | ΔU = Q + W | Schroeder [2000] |
28. | Energy can neither be created nor destroyed; it can only change forms. | Cengel & Boles [2002] |
29. | Energy can be neither created nor destroyed; heat and mechanical work being mutually convertible. | Clark [2004] |
30. | Although energy assumes many forms, the total quantity of energy is constant, and when energy disappears in one form it appears simultaneously in other forms. | Smith, Van Ness & Abbott [2005] |
31. | The total energy after the process is equal to the total energy before the process. | Penrose [2005] |
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