Using Energy in the Real World

A change in any thermodynamic state function is independent of the path used to accomplish that change. This feature of state functions tells us that the energy change in a chemical reaction is independent of the manner in which the reaction takes place. In the real world, chemical reactions often follow very complicated paths. Even a relatively simple overall reaction such as the combustion of CH4 and O2 can be very complicated at the... 

Contemporary scientists have new toy, for the visualization and quantification, called supercomputers. East, reliable, energy consumable, and far from the simple devices, they are the new universal laboratories. This is another proof for the research philosophy of chaos or fractals, first see patterns, then analyze them. Super computers or the ultimate tele-microscope could be used to simulate all of the possible cases of theory or model and to visualize the results. Inputs are collected information, and outputs are transformed information, which can be compared with the information obtained from the experiments in the real world. 

Thermodynamics deals with its subject matter (energy levels, energy changes) in an abstract way. The states and processes it describes are idealized it does not describe or deal with any objects or processes in the real world, except to the extent that the variables in its equations are properties (e.g., volumes, energies) of real substances. Some processes in the real world are very similar to these idealized processes, and some are not. Where they are similar, thermodynamics is directly useful. Where they are not, we invent correction factors (e.g., activity coefficients ) to account for the differences. 

Thermodynamics is the net result of our attempts to do this. It is not a description of any real process but a rather abstract model that can be used for all real processes. Processes in the real world are incredibly complex, but our models of them are quite simple, containing a number of carefully defined concepts. Processes (reactions, changes) involve energy and/or mass changes. 

As we have seen in the last few chapters, this mathematical model of energy relationships is tremendously useful in the real world, basically because even though the real world is in a constant state of flux or change, there are many situations in which it approaches fairly closely a state of equilibrium, and even in cases where it does not, it is changing towards some equilibrium state, and our equilibrium models are useful in many ways. But obviously we would like to know more about the state of flux itself. How fast do the changes we see take place, and what controls this rate of change We enter the world of chemical kinetics. 

Almost every chemical process includes many reaction steps. This means that the reactants will first produce intermediates, which will then be involved in further reactions leading to the final products. Frequently, the final products of the chemical process appear only after several hundreds or thousands of different reaction steps. The products may include those that are desired (e.g. yields of valuable chemicals or energy) and those that are unwanted, such as pollutants. If the stoichiometric equations and the rates of each reaction step are known, then the chemical process can in principle be controlled. In industrial applications this means that the composition of the reacting mixture and the conditions of the reaction process can be selected so that the process operates as efficiently as possible and has low environmental impact. Simulations of detailed reaction mechanisms can therefore be extremely useful within the design phase of new equipment or for the development and control of existing equipment. If a model is accurate and robust, and can be simulated efficiently, then it can be used in place of expensive experiments for process design. Within the book we have tried to address methods that can be used to assess and improve the robustness of kinetic mechanisms, as well as to reduce their impact on the simulation time of models of coupled chemical and physical processes. The aim of all of these methods is to improve the utility of kinetic mechanisms for a range of applications in the real world. 

In our world, most chemical processes occur in contact with the Earth s atmosphere at a virtually constant pressure. For example, plants convert carbon dioxide and water into complex molecules animals digest food water heaters and stoves bum fiiel and mnning water dissolves minerals from the soil. All these processes involve energy changes at constant pressure. Nearly all aqueous-solution chemistry also occurs at constant pressure. Thus, the heat flow measured using constant-pressure calorimetry, gp, closely approximates heat flows in many real-world processes. As we saw in the previous section, we cannot equate this heat flow to A because work may be involved. We can, however, identify a new thermod mamic function that we can use without having to calculate work. Before doing this, we need to describe one type of work involved in constant-pressure processes. 

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