The System and Its Surroundings

The diffcrrential form of the first law as applied to a dosed system, for which there is no exchange of matter between the system and its surroundings, is given by... 

For any reversible process, the sum of the changes in entropy for the system and its surroundings is zero. All natural or real processes are irreversible and are accompanied by a net increase in entropy. 

In any irreversible change, the overall disorder of the system and its surroundings increases, which means that the number of microstates increases. If W increases, then so does In W, and the statistical entropy increases, too. 

By the same reasoning, a negative AS ° and a positive AH ° oppose spontaneity, so a reaction in which the system becomes constrained and energy is absorbed is nonspontaneous regardless of temperature. The system and its surroundings both would experience decreases in entropy if such a process were to occur, and this would violate the second law of thermod3mamics. 

Figure 2a shows the simplest possible model of an operating step, introduced by Fikes and Nilsson (1971) and known as the STRIPS operator. The preconditions are statements that must be true of the system and its surrounding world before the action can be taken. Similarly, the postconditions are statements that are guaranteed to be true after the actions corresponding to the specific operation have been carried out. The allowable forms of pre-, and postconditions should satisfy the following requirements ... 

Just as heat transfer refers to the energy transfer within a system or between a system and its surroundings occurring because of a difference in temperature, mass transfer refers to the transfer of mass (i.e., matter) which occurs within a system or between the system and its surroundings due to a difference in the concentration of a particular component between two points which are not in equilibrium. 

Diffusion—transport of matter as a result of differing values of the chemical potential of a given component at various sites within the system, or in the system and its surroundings. Obviously, the particles... 

Heat conduction—the transport of energy resulting from temperature gradients in the system or difference in temperature, between the system and its surroundings. Heat conduction arises from the fact that, while the number of particles per volume unit is identical at various sites in the system, they have different impulses. 

The inventory tasks is to collect environmentally important information about relevant processes involved in the product system. Inventory collects information about unit processes at first and subsequently, an inventory of inputs and outputs of the system and its surroundings is carried out. The goal is the identification and quantification of all elementary flows associated with product system. Inventory analysis is the nature of the technical implementation of LCA studies. It is an essential part of a study, has high demands for data availability, practical experience in modelling product systems and, in the case of using database tools, it is necessary to master them perfectly and to understand their function [46]. The inventory phase principle is data collection that is used to quantify values of the elementary flows. This phase represents a major practical part of the LCA study, time consuming and with demands for data availability and author s experience with modelling product system studies [47],... 

Consider a closed system (i.e., one in which there is no exchange of matter between the system and its surroundings) where a single chemical reaction may occur according to equation 1.1.3. Initially there are ni0 moles of constituent At present in the system. At some later time there are n moles of species At present. At this time the molar extent of reaction is defined as... 

Adiabatic a system condition in which no heat is exchanged between the system and its surroundings in practice, near adiabatic conditions are reached through good insulation. 

We call the sum of the system and its surroundings the thermodynamic universe (see Figure 4.3). A thermodynamic universe is described as that volume large enough to enclose all the thermodynamic changes . The entropy change of the thermodynamic universe during crystallization is A (totai), which equates to... 

When the system goes from state 1 to state 2, the change in internal energy (AC/) is fixed, but Q and W depend on the path taken. If no heat passes between the system and its surroundings during the process, the change is said to be adiabatic. In an adiabatic process, Q = 0 and AC/ = W. The most usual form of work involved in chemical reactions is volume work, that is work associated with a change in volume of a system, in which case... 

The second law of thermodynamics states that an overall increase must take place in the entropy of the system and its surroundings in any process that occurs spontaneously. An isolated system proceeds spontaneously to states of increasingly greater entropy (greater disorder). 

For a process to be spontaneous, the total entropy of the system and its surroundings must increase. That is,... 

Hence the flow of each chapter of this book will lead from a description of specific chemical/biological processes and systems to the identification of the main state variables and processes occurring within the boundaries of the system, as well as the interaction between the system and its surrounding environment. The necessary system processes and interactions are then expressed mathematically in terms of state variables and parameters in the form of equations. These equations may most simply be algebraic or transcendental, or they may involve functional, differential, or matrix equations in finitely many variables. 

The laws of thermodynamics are statistical laws. This means that they describe large assemblies of particles called systems. The system is defined as some arbitrary part of the universe with defined boundaries. If neither heat nor matter is exchanged between the system and its surroundings, it is called an isolated system. If matter cannot cross the system boundaries, it is said to be a closed system if it can cross, then it is an open system. If it is thermally insulated, it is an adiabatic system. 

The concept behind the defining equation (Eq. (2.37)) comes from an experiment known as the Joule experiment, which is illustrated in Figure 2.3. The result of this experiment is known as the Joule effect. In this experiment the gas is confined in one part of a closed container and the other part is evacuated. The gas itself is taken to be the substance composing the system. However, the boundary between the system and its surroundings is chosen to be the walls of the container. The volume of the system is the total volume of the container and is not the same as the volume of the gas when it is... 

We return to the piston-and-cylinder arrangement discussed in Section 2.3. In that discussion we did not completely describe the process because we were interested only in developing the concept of work. Here, to complete the description, we choose an isothermal process and a gas to be the fluid. We then have a gas confined in the piston-and-cylinder arrangement. A work reservoir is used to exert the external force, Fe, on the piston this reservoir can have work done on it by the expansion of the gas or it can do work by compressing the gas. A heat reservoir is used to make the process isothermal. The piston is considered as part of the surroundings, so the lower surface of the piston constitutes part of the boundary between the system and its surroundings. Thus, the piston, the cylinder, and the two reservoirs constitute the surroundings. 

The first law of thermodynamics cannot be used to predict whether a reaction can occur spontaneously, as some spontaneous reactions have a positive AE. Therefore a function different from AE is required. One such function is entropy (S), which is a measure of the degree of randomness or disorder of a system. The entropy of a system increases (AS is positive) when the system becomes more disordered. The second law of thermodynamics states that a process can occur spontaneously only if the sum of the entropies of the system and its surroundings increases (or that the universe tends towards maximum disorder), that is ... 

However, using entropy as a criterion of whether a biochemical process can occur spontaneously is difficult, as the entropy changes of chemical reactions are not readily measured, and the entropy change of both the system and its surroundings must be known. These difficulties are overcome by using a different thermodynamic function, free energy (G), proposed by Josiah Willard Gibbs which combines the first and second laws of thermodynamics ... 

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