State property entropy

Entropy, like enthalpy (Chapter 8), is a state property. That is, tine entropy depends only on the state of a system, not on its history. The entropy change is determined by the entropies of the final and initial states, not on the path followed from one state to another. 

The most common states of a pure substance are solid, liquid, or gas (vapor), state property See state function. state symbol A symbol (abbreviation) denoting the state of a species. Examples s (solid) I (liquid) g (gas) aq (aqueous solution), statistical entropy The entropy calculated from statistical thermodynamics S = k In W. statistical thermodynamics The interpretation of the laws of thermodynamics in terms of the behavior of large numbers of atoms and molecules, steady-state approximation The assumption that the net rate of formation of reaction intermediates is 0. Stefan-Boltzmann law The total intensity of radiation emitted by a heated black body is proportional to the fourth power of the absolute temperature, stereoisomers Isomers in which atoms have the same partners arranged differently in space, stereoregular polymer A polymer in which each unit or pair of repeating units has the same relative orientation, steric factor (P) An empirical factor that takes into account the steric requirement of a reaction, steric requirement A constraint on an elementary reaction in which the successful collision of two molecules depends on their relative orientation. 

State properties, of mixtures, 24 671-672 State right to know (RTK) laws, ink regulation under, 14 332 State safety acts/regulations, 21 830-831 States, change in entropy between, 24 649 State variables, to fix the properties of a mixture, 24 681—682 STATGRAPHICS plus 5 (quality and design)... 

Any characteristic of a system is called a property. The essential feature of a property is that it has a unique value when a system is in a particular state. Properties are considered to be either intensive or extensive. Intensive properties are those that are independent of the size of a system, such as temperature T and pressure p. Extensive properties are those that are dependent on the size of a system, such as volume V, internal energy U, and entropy S. Extensive properties per unit mass are called specific properties such as specific volume v, specific internal energy u, and specific entropy. s. Properties can be either measurable such as temperature T, volume V, pressure p, specific heat at constant pressure process Cp, and specific heat at constant volume process c, or non-measurable such as internal energy U and entropy S. A relatively small number of independent properties suffice to fix all other properties and thus the state of the system. If the system is composed of a single phase, free from magnetic, electrical, chemical, and surface effects, the state is fixed when any two independent intensive properties are fixed. 

IL-6 There exists a macroscopic state property S ( entropy ) that achieves the character of a maximum with respect to variations that do not alter the energy of an isolated system at equilibrium, and whose differential changes at equilibrium are given by dS = dq/T. 

Recall that entropy is a state property, so A5a >b is independent of whether a reversible or irreversible path was followed.) From (4.45)-(4.47), we conclude finally that... 

It was the principal genius of J. W. Gibbs (Sidebar 5.1) to recognize how the Clausius statement could be recast in a form that made reference only to the analytical properties of individual equilibrium states. The essence of the Clausius statement is that an isolated system, in evolving toward a state of thermodynamic equilibrium, undergoes a steady increase in the value of the entropy function. Gibbs recognized that, as a consequence of this increase, the entropy function in the eventual equilibrium state must have the character of a mathematical maximum. As a consequence, this extremal character of the entropy function makes possible an analytical characterization of the second law, expressible entirely in terms of state properties of the individual equilibrium state, without reference to cycles, processes, perpetual motion machines, and the like. 

The system of our choice will usually prevail in a certain macroscopic state, which is not under the influence of external forces. In equilibrium, the state can be characterized by state properties such as pressure (P) and temperature (T), which are called "intensive properties." Equally, the state can be characterized by extensive properties such as volume (V), internal energy (U), enthalpy (H), entropy (S), Gibbs energy (G), and Helmholtz energy (A). 

The second law is associated with the direction of a process. It defines the fundamental property entropy, S, and states that in any real process the direction of the process corresponds to the direction in which the total entropy increases, that is, the entropy change of both the system and environment should in total result in a positive result or in equation form... 

However, it should not be necessary to make any heat capacity measurements at all, or any assumptions as to the thermal properties of the solid and liquid states in order to calculate the correct value for the entropy of hydrogen. Since hydrogen gas at low temperatures consists entirely of molecules in the zero rotational state, its entropy will be that of a monatomic gas of atomic weight 2.016. The entropy at 298°K. will be obtained by adding the integral f CPd In T over the proper temperature range. The heat capacity may be separated into a constant term 5/2R and the rotational term Cr. 

Let us now consider a steady flow of heat dQ(irr) that occurs irreversibly between a phase at a high temperature T, and a phase at a low temperature T2 in a closed system as shown in Fig. 3.7. The phase 1 continuously receives heat dQ = T1dS1 in a reversible way from the surroundings at temperature Tl and the phase 2 continuously releases heat dQ - T2dS2 into the surroundings at temperature T2. In the steady state no change occurs in the state property of the system except an increase in entropy dSjrr due to the irreversible heat transfer dQ(irr) = dQ ... 

For a closed system the first law of thermodynamics has defined an energy function called internal energy U, which is expressed as a function of the temperature, volume, and number of moles of the constituent substances in the system U = u(t, V, n, nc). Furthermore, the second law has defined a state property, called entropy S, of the system, which is also expressed as a function of state variables S =s(T,V,nl---nc). Thermodynamics presumes that the functions t/(r,V,n, " nj and 5(7, y, I nc) exist independent of whether the system is closed or open. The energy functions of U, H, F, and G, then, apply not only to closed systems but also to open systems. 

Therefore, -S is a state property or an exact differential. Entropy cannot be easily defined but can be described in terms of entropy increase accompanying a particular process. 

Entropy, S A thermodynamic state property that measures the degree of disorder or randomness of a system. 

It may be added here, that, as extensions to these computational predictors of solubility, initial information has been published recently on the search for models for the prediction of drug solubility and permeability, bioavailability and for the determination of the influence of some solid-state properties (melting point, enthalpy of melting and entropy of melting) on the intrinsic solubility of drugs. °... 

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