![]() ![]() ![]() ![]() According to the Boltzmann equation, the entropy of this system is zero. 13.6: The Third Law of Thermodynamics This system may be described by a single microstate, as its purity, perfect crystallinity and complete lack of motion (at least classically, quantum mechanics argues for constant motion) means there is but one possible location for each identical atom or molecule comprising the crystal (Ω=1).By expanding consideration of entropy changes to include the surroundings, we may reach a significant conclusion regarding the relation between this property and spontaneity. Processes that involve an increase in entropy of the system (ΔS > 0) are very often spontaneous however, examples to the contrary are plentiful. 13.5: Entropy Changes and Spontaneity In the quest to identify a property that may reliably predict the spontaneity of a process, we have identified a very promising candidate: entropy.Changes in internal energy, that are not accompanied by a temperature change, might reflect changes in the entropy of the system. 13.4: Entropy Changes in Reversible Processes Changes in internal energy, that are not accompanied by a temperature change, might reflect changes in the entropy of the system.The 2nd law states that in a reversible process, the entropy of the universe is constant and in an irreversible process, the entropy of the universe increases. The change in entropy of the system or the surroundings is the quantity of heat transferred divided by the temperature. In contrast, an irreversible process occurs in one direction only. 13.3: Entropy and Heat - Experimental Basis of the Second Law of Thermodynamics A reversible process is one for which all intermediate states between extremes are equilibrium states it can change direction at any time.The only system that meets this criterion is a perfect crystal at a temperature of absolute zero (0 K), in which each component atom, molecule, or ion is fixed in place within a perfect crystal lattice. A perfectly ordered system with only a single microstate available to it would have an entropy of zero. The greater the molecular motion of a system, the greater the number of possible microstates and the higher the entropy. 13.2: Entropy and Spontaneity - A Molecular Statistical Interpretation These forms of motion are ways in which the molecule can store energy.We’ll also gain insight into how the spontaneity of a process affects the distribution of energy and matter within the system. In doing so, we’ll gain an understanding as to why some systems are naturally inclined to change in one direction under certain conditions and how relatively quickly or slowly that natural change proceeds. 13.1: The Nature of Spontaneous Processes In this section, consider the differences between two types of changes in a system: Those that occur spontaneously and those that occur by force. ![]()
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