For example, distributing four particles among two boxes will result in 2 4 = 16 different microstates as illustrated in (Figure 9.3.2). The number of microstates possible for such a system is n N. This molecular-scale interpretation of entropy provides a link to the probability that a process will occur as illustrated in the next paragraphs.Ĭonsider the general case of a system comprised of N particles distributed among n boxes. Conversely, processes that reduce the number of microstates, W f < W i, yield a decrease in system entropy, S < 0. 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.įor processes involving an increase in the number of microstates, W f > W i, the entropy of the system increases and S > 0. In thermodynamics, a reversible process is one 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 in some condition. This new property was expressed as the ratio of the reversible heat ( q rev) and the kelvin temperature ( T). A later review of Carnot’s findings by 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 9.3.1) 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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