Dispersal of Energy and Matter

Spontaneity is favored when the change causes an increase in the dispersal of energy and matter 

The dispersal of enei in a system results in the energy being spread over many particles rather than being concentrated in just a few. 

To understand this concept, think about a system consisting of just two molecules, A and B, with a total of two units of energy. Denoting one unit of energy with a, we can list the three ways to distribute these two energy units over the two molecules as 

Suppose these two molecules are mixed with two other molecules, C and D, that initially have no energy. When collisions occur, energy can be transferred from one molecule to another. Now the energy can be dispersed among the four molecules in ten different waj  

Now there are obviously more ways (ten) the energy can be dispersed than before. In only three of these ways would all of the energy be distributed as before— A, A B, and B. Put another way, there is only a 3/10 probability that the energy will be restricted to the original molecules, A and B. There are seven ways out of ten, or a probability of 7/10, that at least some of the energy has been transferred to C or D. 

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The Two Aspects of Spontaneity 15-13 Dispersal of Energy and Matter 15-14 Entropy, S, and Entropy Change, AS 15-15 The Second Law ofThermodynamics 15-16 FreeEnergy Change, AG,and Spontaneity... 

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. 

Understand the relationship of entropy to the dispersal of energy and dispersal of matter (disorder) in a system Use tabulated values of absolute entropies to calculate the entropy change, AS ... 

Comprehensive chapters are presented on chemical thermod)mamics (Chapter 15) and chemical kinetics (Chapter 16). The discussion of entropy includes the concepts of dispersal of energy and dispersal of matter (disorder). The distinction between the roles of standard and nonstandard Gibbs free-energy change in predicting reaction spontaneity is clearly discussed. Chapter 15 is structured so that the first nine sections, covering thermochemistry and bond energies, could be presented much earlier in the course. Chapter 16 provides an early and consistent emphasis on the experimental basis of kinetics. 

The measure of the disorderly dispersal of energy or matter used in thermodynamics is called the entropy, S. We shall soon define entropy precisely and quantitatively, but for now all we need to know is that when matter and energy disperse in disorder, entropy increases. That being so, we can combine the two remcuks above into a single statement known is the Second Law of thermodynamics ... 

When the NaCl dissolves, the ions disperse throughout the water. This allows the ions and the water molecules to transfer energy to each other. Dispersal of matter allows for more dispersal of energy. 

In these examples, we see that energy and matter tend to become dispersed (spread out). We shall see that this dispersal is a fundamental driving force that affects the spontaneity of any process. 

SEM studies. The surface morphology of KL and KLd was studied by scanning electron microscopy (SEM) with a JEOL JSM-6400. The microscope was equipped with an energy dispersive X-ray (EDX) microanalyser that was used for observing the dispersion of the mineral matter in KL and KLd. 

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. 

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. 

Processes that do not involve obvious dispersal of matter may nevertheless have preferred directions. For example. Figure 14-3 shows that when a hot block of metal is placed in a cold glass of water, the metal block cools and the water warms. This process continues until the two are at the same temperature. Whenever two objects at different temperatures contact each other, the object at higher temperature transfers energy to the object at lower temperature. 

Spontaneous processes result in the dispersal of matter and energy, hi many cases, however, the spontaneous direction of a process may not be obvious. Can we use energy changes to predict spontaneity To answer that question, consider two everyday events, the melting of ice at room temperature and the formation of ice in a freezer. 

Equations 12.7.48 and 12.7.39 provide the simplest one-dimensional mathematical model of tubular fixed bed reactor behavior. They neglect longitudinal dispersion of both matter and energy and, in essence, are completely equivalent to the plug flow model for homogeneous reactors that was examined in some detail in Chapters 8 to 10. Various simplifications in these equations will occur for different constraints on the energy transfer to or from the reactor. Normally, equations 12.7.48 and 12.7.39... 

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