Energy flow to and from a system

Each particle in a system has potential and kinetic energy, and the sum of these energies for all the particles is the internal energy, E, of the system (some texts use the symbol U). When a chemical system changes from reactants to products 

Note that the change in energy is always an energy transfer from system to surroundings, or vice versa. 

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System and Surroundings Energy Flow to and from a System Heat and Work Energy Conservation Units of Energy State Functions... 

DSC is a precise method of measuring the endothermic and exothermic behaviors of sample materials. Unlike the earlier version of the thermal analyzer, the differential thermometric analyzer (DTA) measures the temperature difference between two cells heating in the same furnace. The power-compensated DSC uses two independent furnaces, one for the sample and one for the reference. When an exothermic or endothermic change occurs in the sample materials, energy is applied to or removed from one or both furnaces to compensate for energy changes in the sample. This means that the system directly measures energy flows to or from a sample at all times. 

Heat energy flows to or from the surroundings when there is a difference in temperature, when a chemical reaction or change of state takes place, or when work is done on or by the system. Unlike P, V, T, and E, heat is not a function of the state of the system. We cannot speak of a system "having heat" q refers only to energy in transit. 

When two bodies are placed in thermal contact and energy flows from the warmer body to the cooler one, we call the process heat . A transfer of energy to or from a system by any means other than heat is called work . 

Hold a system at constant temperature with a heat bath. Although the temperature is fixed, the energy of the system will undergo fluctuations, usually very small, as heat flows to and from the bath. The heat capacity is a measure of the magnitude of these fluctuations. To derive this relationship, we switch our attention from microstates to energy levels (see Chapter 10), so we need the density of states. 

The/low line layout uses the train or line system, which locates all the equipment in the order in which it occurs on the flow sheet. This minimizes the length of transfer lines and, therefore, reduces the energy needed to transport materials. This system is used extensively in the pharmaceutical industry, where each batch of a drug that is produced must be kept separate from all other batches. In other industries it is used mainly for small-volume products.3... 

The problem to be considered now is how to tear effectively a system of such units, units interconnected by material (and probably energy) flows. We assume that the input-output relationships are known for each unit, and that outputs must be calculated from the inputs. Each physical flow corresponds to several variables, and the criterion for tearing will be to minimize the number of variables that must be assumed to solve the torn system, i.e., to have the minimum number of variables associated with the total of the torn streams. 

Soils are multicomponent, multiphase, open systems that sustain a myriad of interconnected chemical reactions, including those involving the soil biota. The multiphase nature of soil derives from its being a porous material whose void spaces contain air and aqueous solution. The solid matrix (which itself is multiphase), soil air, and soil solution—each is a mixture of reactive chemical compounds—hence the multicomponent nature of soil. Transformations among these compounds can be driven by flows of matter and energy to and from the vicinal atmosphere, biosphere, and hydrosphere. These external flows, as well as the chemical composition of soil, vary in both space and time over a broad range of scales. 

L As heat, or energy that flows as a result of temperature difference between a system and its surroundings. The direction of flow is always from a higher temperature to a lower one. Heat is defined as positive when it is transferred to the system from the surroundings. 

Suppose sys(f) is the total energy (internal + kinetic + potential) of a system, and ihm and /hout are the mass flow rates of the system input and output streams. (If the system is closed, these quantities each equal zero.) Proceeding as in the development of the transient mass balance equation, we apply the general energy balance equation (11.3-1) to the system in a small time interval from t to t + 1st, during which time the properties of the input and output streams remain approximately constant. The terms of the equation are as follows (see Section 7,4) ... 

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