As a result, S liquid > S solid and the process of converting a substance from solid to liquid (melting) is characterized by an increase in entropy, Δ S > 0. This increased freedom of motion results in a greater variation in possible particle locations, so the number of microstates is correspondingly greater than for the solid. In the liquid phase, the atoms or molecules are free to move over and around each other, though they remain in relatively close proximity to one another. With essentially fixed locations for the system’s component particles, the number of microstates is relatively small. In the solid phase, the atoms or molecules are restricted to nearly fixed positions with respect to each other and are capable of only modest oscillations about these positions. Consider the phase changes illustrated in Figure 5. The relationships between entropy, microstates, and matter/energy dispersal described previously allow us to make generalizations regarding the relative entropies of substances and to predict the sign of entropy changes for chemical and physical processes. And, again, this spontaneous process is also characterized by an increase in system entropy. This supports the common observation that placing hot and cold objects in contact results in spontaneous heat flow that ultimately equalizes the objects’ temperatures. \Delta S=\frac. As for the previous example of matter dispersal, extrapolating this treatment to macroscopic collections of particles dramatically increases the probability of the uniform distribution relative to the other distributions. In 1865, Clausius named this property entropy ( S) and defined its change for any process as the following: Similar to other thermodynamic properties, this new quantity is a state function, and so its change depends only upon the initial and final states of a system. (a) Nicholas Léonard Sadi Carnot’s research into steam-powered machinery and (b) Rudolf Clausius’s later study of those findings led to groundbreaking discoveries about spontaneous heat flow processes. Note that the idea of a reversible process is a formalism required to support the development of various thermodynamic concepts no real processes are truly reversible, rather they are classified as irreversible.įigure 1. The term reversible process refers to a process that takes place at such a slow rate that it is always at equilibrium and its direction can be changed (it can be “reversed”) by an infinitesimally small change is some condition. This new property was expressed as the ratio of the reversible heat ( q rev) and the kelvin temperature ( T). In a later review of Carnot’s findings, Rudolf Clausius introduced a new thermodynamic property that relates the spontaneous heat flow accompanying a process to the temperature at which the process takes place. In 1824, at the age of 28, Nicolas Léonard Sadi Carnot (Figure 1) published the results of an extensive study regarding the efficiency of steam heat engines. Predict the sign of the entropy change for chemical and physical processes.Explain the relationship between entropy and the number of microstates. By the end of this section, you will be able to:
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