توازن حراري: الفرق بين النسختين

<ref>Gibbs, J.W. (1876/1878). On the equilibrium of heterogeneous substances, ''Trans. Conn. Acad.'', '''3''': 108-248, 343-524, reprinted in ''The Collected Works of J. Willard Gibbs, Ph.D, LL. D.'', edited by W.R. Longley, R.G. Van Name, Longmans, Green & Co., New York, 1928, volume 1, pages 55-353, particularly pages 144-150.</ref><ref>Bailyn, M. (1994). ''A Survey of Thermodynamics'', American Institute of Physics Press, New York, ISBN 0-88318-797-3, pages 254-256.</ref> A system prepared as a mixture of petrol vapour and air can be ignited by a spark and produce carbon dioxide and water; if this happens in an isolated system, it will increase the temperature of the system, and during the increase, the system is not in thermal equilibrium; but eventually the system will settle to a uniform temperature. In a system prepared as a block of ice floating in a bath of hot water, and then isolated, the ice can melt; during the melting, the system is not in thermal equilibrium; but eventually its temperature will become uniform. Such changes in isolated systems are irreversible in the sense that while such a change will occur spontanteously whenever the system is prepared in the same way, the reverse change will never occur spontanteously within the isolated system; this is a large part of the content of the [[second law of thermodynamics]]. Truly isolated systems hardly occur in nature, and nearly always are artificially prepared.