Entropy dispersion

This means that all substances have some entropy (dispersal of energy and/or matter, i.e. disorder) except when the substance is a pure, perfect, motionless, vibrationless crystal at absolute zero Kelvin. This also implies that the entropy of a substance can be expressed on an absolute basis. 

There is an increase in entropy (dispersal of energy) in only the process (c) sublimation of dry ice, C02(s) - C02(g). In the other physical processes, the systems are becoming more ordered and the entropy is decreasing. 

When the volume occupied by one mole of Ar at 0°C is halved, there is a decrease in entropy (dispersal of energy), as signified by the negative sign of the entropy change, -5.76 J/(mol rxn)-K. In the smaller volume there are fewer energy levels available for the argon molecules to occupy and so, there is a decrease in entropy in the smaller volume. 

A general prerequisite for the existence of a stable interface between two phases is that the free energy of formation of the interface be positive were it negative or zero, fluctuations would lead to complete dispersion of one phase in another. As implied, thermodynamics constitutes an important discipline within the general subject. It is one in which surface area joins the usual extensive quantities of mass and volume and in which surface tension and surface composition join the usual intensive quantities of pressure, temperature, and bulk composition. The thermodynamic functions of free energy, enthalpy and entropy can be defined for an interface as well as for a bulk portion of matter. Chapters II and ni are based on a rich history of thermodynamic studies of the liquid interface. The phase behavior of liquid films enters in Chapter IV, and the electrical potential and charge are added as thermodynamic variables in Chapter V. 

When a gas comes in contact with a solid surface, under suitable conditions of temperature and pressure, the concentration of the gas (the adsorbate) is always found to be greater near the surface (the adsorbent) than in the bulk of the gas phase. This process is known as adsorption. In all solids, the surface atoms are influenced by unbalanced attractive forces normal to the surface plane adsorption of gas molecules at the interface partially restores the balance of forces. Adsorption is spontaneous and is accompanied by a decrease in the free energy of the system. In the gas phase the adsorbate has three degrees of freedom in the adsorbed phase it has only two. This decrease in entropy means that the adsorption process is always exothermic. Adsorption may be either physical or chemical in nature. In the former, the process is dominated by molecular interaction forces, e.g., van der Waals and dispersion forces. The formation of the physically adsorbed layer is analogous to the condensation of a vapor into a liquid in fret, the heat of adsorption for this process is similar to that of liquefoction. 

We can expect disorder to increase when a system is heated because the supply of energy increases the thermal motion of the molecules. Heating increases the thermal disorder, the disorder arising from the thermal motion of the molecules. We can also expect the entropy to increase when a given amount of matter spreads into a greater volume or is mixed with another substance. These processes disperse the molecules of the substance over a greater volume and increase the positional disorder, the disorder related to the locations of the molecules. 

Microdomain stmcture is a consequence of microphase separation. It is associated with processability and performance of block copolymer as TPE, pressure sensitive adhesive, etc. The size of the domain decreases as temperature increases [184,185]. At processing temperature they are in a disordered state, melt viscosity becomes low with great advantage in processability. At service temperamre, they are in ordered state and the dispersed domain of plastic blocks acts as reinforcing filler for the matrix polymer [186]. This transition is a thermodynamic transition and is controlled by counterbalanced physical factors, e.g., energetics and entropy. 

The small and positive values of enthalpy of solution of water in AOT-reversed micelles indicate that its energetic state is only slightly changed and that water solubilization (unfavorable from an enthalpic point of view) is driven mainly by a favorable change in entropy (the destructuration of the water at the interface and its dispersion as nanodroplets could be prominent contributions) [87],... 

The function that provides a quantitative measure of dispersal is called entropy and is symbolized S. In 1877, the Austrian physicist Ludwig Boltzmann derived Equation, which defines the entropy of a substance in terms of W, the number of ways of describing the system. 

Although the Boltzmann equation may appear simple, applying it to a molecular system always is challenging. The reason is that there are immense numbers of molecules in any realistic molecular system, so it is necessary to count huge numbers of possibilities to determine the value of W. Instead, scientists have found ways to measure entropy by analyzing energy dispersal. 

Any energy transfer results in either dispersal or constraint of energy, and thus generates a change in entropy (A jS). When a flow of heat occurs at constant temperature. Equation provides a quantitative measure of the... 

The negative sign for the entropy change of the ice/water mixture is consistent with our qualitative view that matter is more dispersed in a liquid than in a solid. The positive sign for the entropy change of the freezer is consistent with heat being absorbed by the freezer, which increases the dispersal of energy. 

More energy is required to heat one mole of argon gas from 87.3 to 298 K, and this energy gets dispersed among the argon atoms, increasing the entropy still further. 

The reason behind this trend is that a molecule with many atoms has more variations in how it can vibrate than a molecule with few atoms. This means more ways to distribute energy—in other words, greater energy dispersal at any given temperature—and larger entropy. 

The decomposition of N2 O4 requires a bond to break. This is the reason why the decomposition has a positive A 77 °. At the same time, the number of molecules doubles during decomposition, which is the reason AS° has a positive value. The positive enthalpy change means that energy Is removed from the surroundings and constrained, whereas the positive entropy change means that matter is dispersed. At temperatures below 315 K, the enthalpy term dominates and decomposition is not spontaneous, but at temperatures above 315 K, the entropy term dominates and decomposition is spontaneous. 

Reactions that have positive AH° and positive A S ° are favored by entropy but dis-favored by enthalpy. Such reactions are spontaneous at high temperature, where the T AS° term dominates A G °, because matter becomes dispersed during the reaction. A reaction is entropy-driven under these conditions. These reactions are nonspontaneous at low temperature, where the A iiT ° term dominates A G °. 

Phase changes, which convert a substance from one phase to another, have characteristic thermodynamic properties Any change from a more constrained phase to a less constrained phase increases both the enthalpy and the entropy of the substance. Recall from our description of phase changes in Chapter 11 that enthalpy increases because energy must be provided to overcome the intermolecular forces that hold the molecules in the more constrained phase. Entropy increases because the molecules are more dispersed in the less constrained phase. Thus, when a solid melts or sublimes or a liquid vaporizes, both A H and A S are positive. Figure 14-18 summarizes these features. 

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