![]() ![]() (A molecule moving at an average speed of around a thousand miles an hour collides with others about seven times in a billionth of a second. That is a more modern view that we will use.) In the next instant the system immediately changes to another microstate. In quantum mechanics the behavior of molecules is only described in terms of their energies on particular energy levels. (This is talking in ‘classical mechanics’ language where molecules are assumed to have location and momentum. One microstate then is something like a theoretical "absolutely instantaneous photo" of the location and momentum of each molecule and atom in the whole macrostate. ![]() Each specific way, each arrangement of the energy of each molecule in the whole system at one instant is called a microstate." In liquids and gases, the particles themselves are constantly redistributing in location as well as changing in the quanta (the individual amount of energy that each molecule has) due to their incessantly colliding, bouncing off each other with (usually) a different amount of energy for each molecule after the collision. "In a system its energy is constantly being redistributed among its particles. In contrast, a microstate for a system is all about time and the energy of the molecules in that system. Thus, a macrostate does not change over time if its observable properties do not change. In calculations involving entropy, the ΔH of any phase change in a substance (“phase change energy”) is added to motional energy, but it is unaltered in ordinary entropy change (of heating, expansion, reaction, etc.) unless the phase itself is changed.Ī macrostate is the thermodynamic state of any system that is exactly characterized by measurement of the system's properties such as P, V, T, H and number of moles of each constituent. *Motional energy includes the translational, rotational, and vibrational modes of molecular motion. But in thermodynamics, a microstate isn't just about a smaller amount of matter', it is a detailed look at the energy that molecules or other particles have.) A microstate is one of the huge number of different accessible arrangements of the molecules' motional energy* for a particular macrostate. (Admittedly, a macrostate always has to involve an amount of matter large enough for us to measure its volume or pressure or temperature, i.e. Instead, they are two very different ways of looking at a system. There might be decreases in freedom in the rest of the universe, but the sum of the increase and decrease must result in a net increase.\)ĭictionaries define “macro” as large and “micro” as very small but a macrostate and a microstate in thermodynamics aren't just definitions of big and little sizes of chemical systems. The freedom in that part of the universe may increase with no change in the freedom of the rest of the universe. Statistical Entropy - Mass, Energy, and Freedom The energy or the mass of a part of the universe may increase or decrease, but only if there is a corresponding decrease or increase somewhere else in the universe.Qualitatively, entropy is simply a measure how much the energy of atoms and molecules become more spread out in a process and can be defined in terms of statistical probabilities of a system or in terms of the other thermodynamic quantities. Statistical Entropy Entropy is a state function that is often erroneously referred to as the 'state of disorder' of a system.Phase Change, gas expansions, dilution, colligative properties and osmosis. Simple Entropy Changes - Examples Several Examples are given to demonstrate how the statistical definition of entropy and the 2nd law can be applied.A microstate is one of the huge number of different accessible arrangements of the molecules' motional energy* for a particular macrostate. ![]() Microstates Dictionaries define “macro” as large and “micro” as very small but a macrostate and a microstate in thermodynamics aren't just definitions of big and little sizes of chemical systems.“Disorder” was the consequence, to Boltzmann, of an initial “order” not - as is obvious today - of what can only be called a “prior, lesser but still humanly-unimaginable, large number of accessible microstate it was his surprisingly simplistic conclusion: if the final state is random, the initial system must have been the opposite, i.e., ordered. ‘Disorder’ in Thermodynamic Entropy Boltzmann’s sense of “increased randomness” as a criterion of the final equilibrium state for a system compared to initial conditions was not wrong. ![]()
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