The Second Law of Thermodynamics Entropy

These examples are manifestations of one principle the natural tendency of things (in our examples heat, matter, and coherence) to disperse. This is related to the tendency of storing the constant amount of energy of the universe in as many ways as possible. This is the quintessence of the second law of thermodynamics. 

Entropy, 5, is the central notion in the second law. The entropy of a system is a measure of the number of ways that the energy can be stored in that system. In view of the foregoing, any spontaneous process goes along with an entropy increase in the universe (=system + enviromnent) that is, AS 0. If as a result of a process the entropy of a system decreases, the entropy of the environment must increase in order to satisfy the requirement AS 0. 

Based on statistical mechanics, the entropy of a system at constant U and V can be expressed by Boltzmann s law  

Q is the number of states accessible to the system is Boltzmann s constant 

For a given state, Q is fixed and, hence, so is S. It follows that 5 is a function of state. It furthermore follows that 5 is an extensive property for a system comprising two subsystems (a and b) Q = x Qj, and therefore, because of Equation 3.5,S = S + S.  

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In irreversible thermod3mamics, the second law of thermodynamics dictates that entropy of an isolated system can only increase. From the second law of thermodynamics, entropy production in a system must be positive. When this is applied to diffusion, it means that binary diffusivities as well as eigenvalues of diffusion matrix are real and positive if the phase is stable. This section shows the derivation (De Groot and Mazur, 1962). 

It seems enigmatic that we often struggle so hard to achieve desired separations when the basic concept of moving one component away from another is inherently so simple. Much of the difficulty arises because separation flies in the face of the second law of thermodynamics. Entropy is gained in mixing, not in separation. Therefore it is the process of mixing that occurs spontaneously. To combat this and achieve separation, one must apply and manipulate external work and heat and allow dilution in a... 

Statement of the Second Law of Thermodynamics Entropy Changes and Entropy Creation. 

Nukulov AV, Sheehan DP, editors. Special Issue Quantum Limits to the Second Law of Thermodynamics. Entropy. March 2004 Vol. 6, Issue 1. 

According to the second law of thermodynamics, entropy production must be positive. Consequently, the graph of the constitutive relation must be within the first and third quadrant. 

Realizing the shortcomings in the enthalpy-based method, Kenney (1984) proposed to value steam based on the potential work that the steam possesses in comparison with enthalpy. Kenney pointed out that the enthalpy-based pricing method is based on the first law of thermodynamics (energy conservation), while the work-based pricing is based on the second law of thermodynamics (entropy). In thermodynamics, potential work is also termed as availability (a) implying the amount of potential work available. 

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