Closed Systems
Closed systems in chemistry refer to systems where no matter can enter or leave the system, but energy can be exchanged with the surroundings. This means that the total amount of matter within the system remains constant, but there can be changes in energy. Closed systems are often used in chemical experiments and industrial processes to study the behavior of substances under controlled conditions.
7 Key excerpts on "Closed Systems"
eBook - ePub- Jeffrey Gaffney, Nancy Marley(Authors)
- 2017(Publication Date)
- Elsevier(Publisher)
...The kinetics of chemical reactions will be discussed in Chapter 9. Thermodynamics is based on three laws and the concept of thermal equilibrium. The first law of thermodynamics is the application of conservation of energy to the system. The second law addresses the importance of order or disorder in the system, and the third law addresses the order of the system at a temperature of absolute zero. We will further define these laws and examine them in detail as they relate to chemical reactions and processes in Sections 8.2, 8.6, and 8.8. The concept of thermal equilibrium describes the condition between two systems where no heat flows between them when they are connected by a path that can transfer heat. If two systems are in thermal equilibrium with a third system, then they are in thermal equilibrium with each other. A system that is in thermal equilibrium is aid to be adiabatic, where heat neither enters nor leaves the system. In order to describe these chemical systems in a bulk sense, we will first need to define a few terms. The most basic is the definition of a system, which is the part of the universe that is being studied that consists of a number of elements or bodies. It can be small or very large, but has to be part of the universe. The regions outside of the system, essentially the rest of the universe, are considered to be the surroundings. A system can be a closed system or an open system. A closed system is one where mass cannot be exchanged between the system and the surroundings. An open system is one that can readily exchange matter with its surroundings. So, an open system can be influenced by its surroundings. So, experiments that measure thermodynamic properties need to take the surroundings into consideration. Experimental designs require that the interaction with the surroundings be limited and so the system being studied should be as close to a closed system as possible. A system is described by its properties...
eBook - ePub- Gavin Whittaker, Andy Mount, Matthew Heal(Authors)
- 2000(Publication Date)
- Taylor & Francis(Publisher)
...However, there are limitations to the practical scope of thermodynamics which should be borne in mind. Consideration of the energetics of a reaction is only one part of the story. Although hydrogen and oxygen will react to release a great deal of energy under the correct conditions, both gases can coexist indefinitely without reaction. Thermodynamics determines the potential for chemical change, not the rate of chemical change—that is the domain of chemical kinetics (see Topics F1 to F6). Furthermore, because it is such a common (and confusing) misconception that the potential for change depends upon the release of energy, it should also be noted that it is not energy, but entropy which is the final arbiter of chemical change (see Topic B5). Thermodynamics considers the relationship between the system —the reaction, process or organism under study—and the surroundings —the rest of the universe. It is often sufficient to regard the immediate vicinity of the system (such as a water bath, or at worst, the laboratory) as the surroundings. Several possible arrangements may exist between the system and the surroundings (Fig. 1). In an open system, matter and energy may be interchanged between the system and the surroundings. In a closed system, energy may be exchanged between the surroundings and the system, but the amount of matter in the system remains constant. In an isolated system, neither matter nor energy may be exchanged with the surroundings. A system which is held at constant temperature is referred to as isothermal, whilst an adiabatic system is one in which energy may be transferred as work, but not as heat, i.e. it is thermally insulated from its surroundings. Chemical and biological studies are primarily concerned with closed isothermal systems, since most processes take place at constant temperature, and it is almost always possible to design experiments which prevent loss of matter from the system under study. Fig...
eBook - ePub- Mike Pauken(Author)
- 2011(Publication Date)
- For Dummies(Publisher)
...See, you’ve used thermodynamics without even realizing it! This chapter introduces you to thermodynamic analysis of some simple processes involving heat and work for open systems. The concepts using the first law of thermodynamics I discuss here are similar to the ones presented in Chapter 5 for Closed Systems. The difference between an open system and a closed system is whether or not a fluid is allowed to flow into or out of a system. You may be able to guess by their names that a fluid can’t flow in a closed system, but it can flow in an open system. Some examples of simple open systems include heat exchangers, pumps, compressors, turbines, and nozzles. These devices are used in more complicated systems such as power plants, air-conditioning systems, and jet engines, which I discuss in Chapters 10–13. Conserving Mass in an Open System The best way to begin every thermodynamic analysis is by defining a system. A system describes a region enclosed by an imaginary boundary (which may be fixed or flexible) that contains a mass or volume to use for analysis. A system that doesn’t allow mass to enter or leave is called a closed system. The mass inside a closed system is often called the control mass. A system that allows mass to enter and leave is called an open system. The volume of an open system is often called the control volume. This chapter focuses on thermodynamic analysis using the conservation of mass and conservation of energy for open systems. Conservation of mass means that the mass flow rate of material entering a system minus the mass flow rate leaving equals the mass that may accumulate within the system, as described by this equation: When you see a “dot” over a variable like mass (), the dot means that the variable is on a rate basis or per unit time...
eBook - ePubBiomolecular Thermodynamics
From Theory to Application
- Douglas Barrick(Author)
- 2017(Publication Date)
- CRC Press(Publisher)
...In most cases, such samples will be able to exchange one or more forms of energy and/or matter with the environment. Thus, to develop an understanding of thermodynamics and its applications, we need precise definitions that specify our sample (which we refer to as “the system”), the environment (which we refer to as “the surroundings”), and the extent to which the system and surroundings interact (through thermal, mechanical, and material transfer). The system is defined as the part of the universe we choose to study. In biothermodynamics, the system is usually an aqueous solution with various macromolecules, assemblies, and small molecules. However, systems can also be simpler, such as a vessel containing a gas, a pure liquid, or a solid, or can be more complex, for example, a living cell, a whole multicellular organism, or a planet. The surroundings is defined as rest of the universe. Fortunately, from a practical point of view, we do not need to concern ourselves with the entire universe. Rather, we focus on that part of the universe that exchanges matter and energy with the system (i.e., the immediate vicinity), although in some cases, distant sources of energy must be included. † The boundary is defined as border between the system and surroundings. The boundary’s job is to permit (or prevent) interaction between the system and surroundings in terms of exchange of material, heat flow, and volume change (for now we will ignore external fields and exotic kinds of work such as that resulting from stirrers and electrical resistors). The boundary is typically regarded as being thermodynamically negligible, that is, it takes up no volume, has no heat capacity, and does not release or adsorb material...
eBook - ePub- H. W. Liepmann, A. Roshko(Authors)
- 2013(Publication Date)
- Dover Publications(Publisher)
...Thermodynamics predicts the pressure and temperature in this final state easily. Fluid mechanics of a real fluid should tackle the far more difficult task of computing the pressure, temperature, etc., as a function of time and location within the container. For large times, pressure and temperature will approach the thermodynamically given values. Sometimes we need only these final, equilibrium values and hence can make very good use of thermodynamic reasoning even for problems that involve real fluid flow. In fluid mechanics of low-speed flow, thermodynamic considerations are not needed: the heat content of the fluid is then so large compared to the kinetic energy of the flow that the temperature remains nearly constant even if the whole kinetic energy is transformed into heat. In modern high-speed flow problems, the opposite can be true. The kinetic energy can be large compared to the heat content of the moving gas, and the variations in temperature can become very large indeed. Consequently the importance of thermodynamic concepts has become steadily greater. The chapter therefore includes material that is more advanced and not needed for the bulk of the later chapters. Articles that are starred can be omitted at first reading without loss of continuity. 1.2 Thermodynamic Systems A thermodynamic system is a quantity of matter separated from the “surroundings” or the “environment” by an enclosure. The system is studied with the help of measurements carried out and recorded in the surroundings. Thus a thermometer inserted into a system forms part of the surroundings. Work done by moving a piston is measured by, say, the extension of a spring or the movement of a weight in the surroundings. Heat transferred to the system is measured also by changes in the surroundings, e.g., heat may be transferred by an electrical heating coil...
eBook - ePub- Dov M. Gabbay, Paul Thagard, John Woods(Authors)
- 2011(Publication Date)
- North Holland(Publisher)
...Its main use in thermodynamics is in establishing an entropy scale. In 1931 Fowler raised the postulate regarding the existence of thermal equilibrium to the status of the zeroth law of thermodynamics. We need discuss neither the zeroth or the third laws here. In thermodynamics an object of interest is called a system. A system may be isolated (exchanges neither matter nor energy with the surroundings), closed (exchanges only energy with the surroundings) or open (exchanges both energy and matter with surroundings). An equilibrium state of the system (or simply state) is one in which pressure, temperature and chemical potentials have the same value in every part of the system, whether the system is homogeneous (single phase) or heterogeneous (multiple phases). These properties which determine the equilibrium state are called intensive properties or variables. They do not depend on the size of the system and have the same numerical value at each point in space and time. Extensive variables, on the other hand, are proportional to the size of the system. Imagine partitioning a system without altering the conditions. The mass and volume of the system are sums of the corresponding quantities of the parts; pressure, temperature and chemical potentials are not. What is said about pressure, temperature and chemical potentials is also true for density and concentration, except that density and concentration need not have the same value in different phases of the system. Thus density and concentration do not characterize equilibrium states. To distinguish uniform properties that determine the equilibrium state from uniform properties that do not, the former are referred to as intensive fields or just intensities. 2.1. The First Law of Thermodynamics The first law asserts the following: (a) Energy is conserved...
- Kevin Reel, Derrick C. Wood, Scott A. Best(Authors)
- 2014(Publication Date)
- Research & Education Association(Publisher)
...Chapter 10 Thermochemistry Energy Thermochemistry gives consideration to the fact that energy changes occur during chemical reactions. Energy (E) is defined as the ability do work (w) on a system. From a chemistry perspective, kinetic energy comes in the form of translational, vibrational, and rotational motion of molecules, whereas potential energy arises from chemical bonds and electrostatic interactions. Energy cannot be measured directly and is monitored through changes (ΔE). First Law of Thermodynamics The first law of thermodynamics is commonly called the law of conservation of energy: “energy cannot be created or destroyed.” Energy can only be converted from one form into another during chemical reactions, and therefore the energy of the universe is constant. Energy transfers occur between the system (the reaction we are studying) and the surroundings (everything else in the universe). Heat, Temperature, and Enthalpy In the realm of thermochemistry, there are three frequently used terms that are distinctly different from one another: temperature, heat, and enthalpy. Temperature (T) is a measure of the average kinetic energy of molecules, which means that at higher temperatures molecules are moving faster. On the other hand, heat (q) measures the total kinetic energy of all of the particles in a sample. We use temperature as a means to monitor heat transfers. Heat transfers are kinetic energy transfers that go from a hotter object to a cooler object until both objects are at the same temperature. According to the first law of thermodynamics, heat lost by a hotter object is gained by a colder object. In contrast, enthalpy (H) refers to the energy released or absorbed by a chemical reaction. Unless there is pressure–volume (PΔV) work performed by the system, changes in enthalpy (ΔH) are essentially the same as the heat exchanged during a reaction...
