A room is not heated by increasing its internal energy but by decreasing its entropy due to the fact that during heating, the volume and pressure remain constant and air is expelled. We first present a simple solution treating the air in the room as an ideal gas. We calculate the differential entropy change and heat transfer and give numbers for a typical room including estimates of heat loss through windows and walls. We also demonstrate the power of thermodynamics to derive the entropy and internal energy changes for any gas.
REFERENCES
1.
The Swiss physicist
Robert
Emden
(1862–1940) was, successively, a professor of physics, meteorology, and astrophysics at the Technical University of Munich. His work Gaskugeln: Anwendungen der Mechanischen Wärmetheorie auf Kosmologische und Meteorologische Probleme (Gaseous Spheres, The Application of Thermodynamics to Cosmological and Meteorological Problems)
(Teubner
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, laid the foundations of atmospheric science and astrophysics and became the cornerstones of most textbooks on these subjects. He also laid the foundations of the theory of balloon flight and while considering atmospheric radiation, anticipated in 1921 Bose–Einstein statistics for photons in his work on “light quanta.”For more information on this remarkable scientist, see ⟨www.encyclopedia.com/doc/1G2-2830901313.html⟩.
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For -values of insulation and building materials, see, for example, ⟨enwikipedia.org/wiki/R-value_insulation⟩.
10.
We point out some flaws in Ref. 4 so that readers do not become unnecessarily confused. This article has the subtitle, “Illustrating the first law of thermodynamics.” This subtitle is misleading because the energy in the room is conserved only within the model of an ideal gas. Otherwise, energy is conserved in the supersystem of room plus environment. Furthermore, the process of heating the room is driven by entropy. Along with this article are some comments by Wilbur B. Bridgman, which are misleading. We point out two major concerns: His Eq. (9) is mathematically inconsistent because the left-hand side is a differential and the right-hand side is a ratio of two differentials. The proper expression is our Eq. (21). Also the discussion of the crucial role of the reference state (emphasized in the statement at the end of his second to last paragraph “different conclusions are reached depending on the choice of reference state”) is incorrect because thermodynamic predictions cannot depend on the choice of a reference state, but are given by the integrals of differentials.
11.
The highest pressure ever recorded on Earth was 1.07 atm in Agata, Siberia on December 31,
1968
with a temperature of . See ⟨enwikipedia.org/wiki/Atmosphere_pressure⟩.© 2011 American Association of Physics Teachers.
2011
American Association of Physics Teachers
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