Author: workhouse123
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Chemical Potential and Equilibrium
All naturally occurring processes proceed spontaneously until the state of equilibrium is reached where no further net change occurs in the system. The implication of the equilibrium conditions is that the system is not interacting with the surroundings [4]. Understanding this implication is crucial to distinguish between a system at equilibrium and an open system at steady state.…
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Property Changes in Transformations
A system’s properties change when it moves from one state to another. This transformation or process of changing state is inevitably accompanied by heat and work exchange as governed by the first law. When the work and heat effects associated with the process are such that it is feasible to restore the system to its original…
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Enthalpy and Free Energies
As interconversion between heat and work is the central concern of thermodynamics, it is useful to define thermodynamic properties that are related to the heat content of a system and energy available for conversion to work. This consideration leads to three thermodynamic functions or properties that are mathematically defined as follows: 4. The terms Helmholtz function (or Helmholtz…
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Internal Energy and Entropy
Following is the mathematical statement of the first law of thermodynamics for a system, neglecting the changes in the mechanical (kinetic and potential) energy: In this equation, Q is the heat added to the system; W, the work done by the system; and ΔU, the change in the internal energy. The internal energy U can be visualized as the kinetic…
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Fundamental Concepts of Thermodynamics
The formal concepts of thermodynamics are subtle and require much thought before they are comprehended fully or adequately [2]. The development of these concepts is based on a strong foundation in chemistry, physics, and mathematics, built over several semesters of study. Such development is not attempted here; rather, some essential thermodynamic quantities are introduced in…
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Basic Energy Balance Problems
A chemical engineer has to perform a wide variety of energy balance computations for a large number of transformations and processes. These computations require application of the principles discussed in section 7.1. The myriad energy balance computations performed by chemical engineers can very broadly be classified into two types: those involving determination of heat effects in…
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Enthalpy and Heat Capacity
Enthalpy is a measure of the energy (or heat) content of a substance [3]. It is a thermodynamic quantity whose absolute value cannot be determined; however, enthalpy of a substance with respect to its value at some reference conditions can be calculated [4, 5]. The reference state, also called the standard state, is specified in terms of pressure and temperature of…
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Generalized Energy Balance
Consider an arbitrary process represented by the block flow diagram shown in Figure 7.1. Figure 7.1 Energy balance on a process unit; Streams: 1—Inlet, 2—Outlet, 3—Heat, 4—Work. This diagram is similar to the one shown in Figure 6.1 for the material balance, except for the following important differences: First, the streams represent energy flows rather than material flows. The…
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Quantitative Principles of Energy Balance
Because energy can take several different forms, it is necessary for us to understand the forms that are of primary interest to a chemical engineer. These forms are briefly described in the following section. 7.1.1 Forms of Energy Three primary forms of energy are encountered in a chemical process [1]: 1. Kinetic energy (KE)—Energy associated with motion.…
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Material Balances over Multiple Process Units
The incompleteness of the desired reaction and the occurrence of undesired side reaction introduced additional levels of complexity in the simple combustion process previously described. By now, readers should have developed a sense of the enormity of computational tasks for a chemical process plant, considering that a chemical process typically has a large number of…