Engine Efficiency, Entropy, and the Second Law

The first law of thermodynamics seems to allow many thermal phenomena that are not observed experimentally. Indeed, the high symmetry of first-law-type relationships such as (3.99) would seem to suggest that the time sequence between initial and final states of a thermal process could be arbitrarily reversed with no special consequence (other than the expected sign change of AH). Yet experience says that this is not so. 

Reverse-Rumford. As noted in Sidebar 3.1, Count Rumford observed that the work performed by a horse on the cannon-bore was exactly compensated by the heat expelled from the cannon-bore to the surroundings, demonstrating the heat/work equivalence demanded by the first law. Imaginably, the process might have occurred in the opposite direction, with heat added to the cannon-bore (e.g., from a blow-torch) appearing as equivalent work performed on the horse (e.g., driving it backward in its hoofprints), in equal harmony with the first law. Yet such a reverse-Rumford process has never been observed. 

Reverse Heat Flow. Joseph Black s observations (Section 3.4) establish that two 

Evidently, the exact reverse of this process, in which two equal-T samples spontaneously exchange q to warm one sample and cool the other by a compensating amount, would be equally in compliance with the first law. Yet such reverse heat flow has never been observed. 

Reverse Solvation. As described in Section 3.6.7, when a solid crystal of a Na2S04(1v) is placed in water, the crystal spontaneously dissolves with emission of heat q  

Reverse Heat Flow. Joseph Black s observations (Section 3.4) establish that two samples 6), S2 of equal heat capacity but different initial temperatures 7), T2 can exchange equal quantities of heat q to achieve equal and opposite heating/cooling effects to final 7 lv = (I + T2), with no change in the surroundings  

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