Entropy of the universe

Equation (A2.1.21) includes, as a special case, the statement dS > 0 for adiabatic processes (for which Dq = 0) and, a fortiori, the same statement about processes that may occur in an isolated system (Dq = T)w = 0). If the universe is an isolated system (an assumption that, however plausible, is not yet subject to experimental verification), the first and second laws lead to the famous statement of Clausius The energy of the universe is constant the entropy of the universe tends always toward a maximum. ... 

Because the gas in the Carnot cycle starts and ends at the same state, the system s entropy does not change during a cycle. Now apply the second law to the universe for the case of the Carnot cycle. Because the processes are reversible, the entropy of the universe does not change by Equation 2b. This can be written ... 

Equation 5, DS = 0 = —Qn/T , which is impossible since Q = W is not zero and this implies the entropy of the universe would decrease. 

Thermodynamic, second law The entropy of the universe increases in a spontaneous process and remains unchanged in a reversible process. It can never decrease. 

If the system is not isolated, its entropy may either increase or decrease. Thus, if a mass of gas is compressed in a cylinder impervious to heat, its entropy increases, but if heat is allowed to pass out into a medium, the entropy of the gas may decrease. By including the"gas and medium in a larger isolated system, we can apply (10) of 45, and hence show Jhat the medium gains more entropy than the gas loses. An extended assimilation of this kind shows that, if every body affected in a change is taken into account, the entropy of the whole must increase by reason of irreversible changes occurring in it. This is evidently what Clausius (1854) had in mind in the formulation of his famous aphorism The entropy of the universe strives towards a maximum. The word universe is to be understood in the sense of an ultimately isolated system. 

Entropy is an important concept in chemistry because we can use it to predict the natural direction of a reaction. However, not only does the entropy of the reaction system change as reactants form products, but so too does the entropy of the surroundings as the heat produced or absorbed by the reaction enters or leaves them. Both the entropy change of the system and that of the surroundings affect the direction of a reaction, because both contribute to the entropy of the universe. We explore the contribution of the system in this section and the contribution of the surroundings in the next section. 

The first law of thermodynamics states that energy is neither created nor destroyed (thus, The energy of the universe is constant ). A consequence of the second law of thermodynamics is that entropy of the universe increases for all spontaneous, that is, naturally occurring, processes (and therefore, the entropy of the universe increases toward a maximum ). 

The simplest rules of thermodynamics suggest that energy must be expended to do work— You cannot get something for nothing, and that even if work is done some energy is forever lost to useful work— You cannot even get what you paid for . And that this entropy effect is such that the entropy of the universe is forever driving toward a maximum— Nature spontaneously falls into a mess Humor aside, the consequence is that any narrow packet as described above will spread over space in an attempt to make the local and universal mole fraction of A, B or C. .. the same everywhere. 

The second law of thermodynamics involves a term called entropy. Entropy is a measure of the degree that energy disperses from a localized state to one that is more widely spread out. We may also think of entropy (S) as a measure of the disorder of a system. The second law of thermodynamics states that all processes that occur spontaneously move in the direction of an increase in entropy of the universe (system + surroundings). For a reversible process, a system at equilibrium, ASuniverse = 0. We can state this as ... 

According to this second law, the entropy of the universe is continually increasing. The third law of thermodynamics states that for a pure crystalline substance at 0 K the entropy is zero. 

Second Law of Thermodynamics The Second Law of Thermodynamics states that all processes that occur spontaneously move in the direction of an increase in entropy of the universe (system + surroundings). 

The answer to this question involves changes to the surroundings. Each of you, on your way to class, metabolized energy. The movement and heat from your bodies added to the entropy of the air particles around you. In fact, the increase in the entropy of the surroundings was greater than the decrease in the entropy of the system. Therefore, the total entropy of the universe increased. 

The energy of the universe is constant, and the entropy of the universe tends to a maximum. ... 

Today we would hesitate to comment on the energy or entropy of the universe, because we have no way to measure these quantities, and we would refer only to the surroundings that are observed to interact with the system. Some cosmological theorists have suggested that the increase in entropy posmlated by the second law is a result of the expansion of the universe [6]. One recent set of astronomical measurements leads to a prediction that the universe will continue to expand, and another predicts that expansion will reach a maximum and reverse [7]. 

A simple statement of the Second Law is natural processes are accompanied by an increase in the entropy of the universe. There are several other statements of the Second Law in the chapter Notes. As noted above, entropy is a measure of disorder the greater the extent of disorder, the greater the entropy. The Second Law tells us that things change spontaneously in a way that increases disorder. At equilibrium, entropy is maximized and disorder reigns. 

Ions or molecules flowing down their concentration gradients is one aspect of a very general statement known as the Second Law of Thermodynamics. The Second Law is a mathematical statement to the effect that all real processes increase the disorder, captured in a quantity known as entropy, of the universe. Entropy is a measure of disorder or randomness and may be thought of as negative information. 

Second Law of Thermodynamics natural processes are accompanied by an increase in the entropy of the universe. 

The second law is sometimes stated in another way The entropy of the universe always increases. 

A third statement of the second law is based on the entropy. In reversible systems all forces must be opposed by equal and opposite forces. Consequently, in an isolated system any change of state by reversible processes must take place under equilibrium conditions. Changes of state that occur in an isolated system by irreversible processes must of necessity be spontaneous or natural processes. For all such processes in an isolated system, the entropy increases. Clausius expressed the second law as The entropy of the universe is always increasing to a maximum. Planck has given a more general statement of the second law Every physical and chemical process in nature takes place in such a way as to increase the sum of the entropies of all bodies taking any part in the process. In the limit, i.e., for reversible processes, the sum of the entropies remains unchanged. 

The state function which measures disorder is the entropy, S, and the second law of thermodynamics may be stated as follows The entropy of the universe or of an isolated system always increases when a spontaneous irreversible process occurs entropy remains constant in a reversible process, i.e., a process which remains at equilibrium for every step along the way,... 

In contrast to the conservation of internal energy (Eq. 2.1, the first law of thermodynamics), the entropy of the Universe always increases (Eq. 2.5), which is an alternative definition of the second law of thermodynamics. Inherent in the concept of entropy is a preferred direction for spontaneous change (AS rr > 0). For example, at 1 bar pressure, ice melts at 10°C, water freezes at —10°C, and not vice versa. A spontaneous process leads from a state of lower probability to a state of higher probability, and equilibrium is the state of maximum probability (Pitzer, 1995). 

For all practical purposes, we can state that all spontaneous processes in nature result in an increase in the entropy of the universe. We can also generalize with the statement that any system (even the universe) will tend to run down over time (tend in increase in entropy until total chaos—disorder—is reached). 

The Second Law is sometimes stated as the Entropy Law. Entropy is a measure of randomness or disorder in a system. Systems that are more randomized, chaotic, or evenly mixed have more entropy. The Second Law states the entropy of the universe is constantly increasing. One clear implication of the Second Law is that the universe never, and a system almost never, spontaneously becomes more organized. So, hot molecules will not spontaneously separate themselves from cold molecules. Mixtures of oxygen and nitrous oxide will not spontaneously separate and send the oxygen to the patient separately from the nitrous oxide. IV fluids will mix evenly throughout the circulatory system, and not congregate in just the left arm. 

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