![]() ![]() Use the information below to generate a citation. Then you must include on every digital page view the following attribution: If you are redistributing all or part of this book in a digital format, Then you must include on every physical page the following attribution: If you are redistributing all or part of this book in a print format, Want to cite, share, or modify this book? This book uses the Because the amount of heat that can be removed from the system becomes vanishingly small, we expect that the change in entropy of the system along an isotherm approaches zero, that is, But we can certainly ask what happens to the entropy of a system when we try to cool it down to 0 K. The reason a system is unable to reach 0 K is fundamental and requires quantum mechanics to fully understand its origin. This produces a very interesting question in physics: Do we know how a system would behave if it were at the absolute zero temperature? In other words, the temperature of any given physical system must be finite, that is, T > 0 T > 0. One of the common statements of the third law of thermodynamics is: The absolute zero temperature cannot be reached through any finite number of cooling steps. Like the second law of thermodynamics, the third law of thermodynamics can be stated in different ways. In actual experiments, physicists have continuously pushed that limit downward, with the lowest temperature achieved at about 1 × 10 −10 K 1 × 10 −10 K in a low-temperature lab at the Helsinki University of Technology in 2008. This is a statement of the third law of thermodynamics, whose proof requires quantum mechanics that we do not present here. What happens to the entropy of a system at the absolute zero temperature? It turns out the absolute zero temperature is not reachable-at least, not though a finite number of cooling steps. But what happens if the temperature goes to zero, T → 0 T → 0? It turns out this is not a question that can be answered by the second law.Ī fundamental issue still remains: Is it possible to cool a system all the way down to zero kelvin? We understand that the system must be at its lowest energy state because lowering temperature reduces the kinetic energy of the constituents in the system. For any other thermodynamic system, when the process is reversible, the change of the entropy is given by Δ S = Q / T Δ S = Q / T. The second law of thermodynamics makes clear that the entropy of the universe never decreases during any thermodynamic process. Discuss how this result can be related to an increase in disorder of the system. The net result is an increase in entropy and an increase in the disorder of the universe.Ĭheck Your Understanding In Example 4.7, the spontaneous flow of heat from a hot object to a cold object results in a net increase in entropy of the universe. However, this ordering process is more than compensated for by the disordering of the rest of the universe. After all, a single cell gathers molecules and eventually becomes a highly structured organism, such as a human being. You might suspect that the growth of different forms of life might be a net ordering process and therefore a violation of the second law. The increased disorder of the ice more than compensates for the increased order of the reservoir, and the entropy of the universe increases by 4.6 J/K. However, the reservoir’s decrease in entropy is still not as large as the increase in entropy of the ice. Although the change in average kinetic energy of the molecules of the heat reservoir is negligible, there is nevertheless a significant decrease in the entropy of the reservoir because it has many more molecules than the melted ice cube. The molecular arrangement has therefore become more randomized. The ice changes from a solid with molecules located at specific sites to a liquid whose molecules are much freer to move. This process also results in a more disordered universe. If we considered only the phase change of the ice into water and not the temperature increase, the entropy change of the ice and reservoir would be the same, resulting in the universe gaining no entropy. The entropy of the universe therefore is greater than zero since the ice gains more entropy than the reservoir loses.
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