Nonspontaneous (spontaneous in opposite direction)įor many realistic applications, the surroundings are vast in comparison to the system. The Second Law of Thermodynamics Δ S univ > 0 A summary of these three relations is provided in Table 1. These results lead to a profound statement regarding the relation between entropy and spontaneity known as the second law of thermodynamics: all spontaneous changes cause an increase in the entropy of the universe. This process involves no change in the entropy of the universe. In this case, the system and surroundings experience entropy changes that are equal in magnitude and therefore sum to yield a value of zero for Δ S univ. The temperature difference between the objects is infinitesimally small, T sys ≈ T surr, and so the heat flow is thermodynamically reversible.This process involves a decrease in the entropy of the universe. The magnitude of the entropy change for the surroundings will again be greater than that for the system, but in this case, the signs of the heat changes will yield a negative value for Δ S univ.
The arithmetic signs of q rev denote the gain of heat by the system and the loss of heat by the surroundings.
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