Internal energy heat, and work

Experimental observation 4 (Sec. 1.5). A flow of heat and a flow of work are equivalent in that supplying a given amount of energy to a system in either of these forms can be made to result in the same increase ip its internal energy. Heat and work, or niore generally, thermal-and mechanical energy, are not equivalent in the sense... 

Unlike internal energy, heat and work are properties only of the process, not of the state, so they are not state functions. In Example 7.1, for instance, the initial and final states are the same in parts (a) and (b), but the amount of woik done is different because the external, opposing pressures are different. We cannot write Aw = Wf - W for a change. Work done depends not only on the initial state and final state, but also on how the process is carried out, that is, the amount of work done depends on the path. 

TABLE 2.2 Summary of Expressions for Change in Internal Energy, Heat, and Work for an Ideal Gas Undergoing a Reversible Process... 

Experimental observations (>Sec. 1.5). In any change of state the total energy—which includes internal, potential, and kinetic energy, heat, and work—is a conserved quantity. ... 

Pure thermodynamics is developed, without special reference to the atomic or molecular structure of matter, on the basis of bulk quantities like internal energy, heat, and different types of work, temperature, and entropy. The understanding of the latter two is directly rooted in the laws of thermodynamics— in particular the second law. They relate the above quantities and others derived from them. New quantities are defined in terms of differential relations describing material properties like heat capacity, thermal expansion, compressibility, or different types of conductance. The final result is a consistent set of equations and inequalities. Progress beyond this point requires additional information. This information usually consists in empirical findings like the ideal gas law or its improvements, most notably the van der Waals theory, the laws of Henry, Raoult, and others. Its ultimate power, power in the sense that it explains macroscopic phenomena through microscopic theory, thermodynamics attains as part of Statistical Mechanics or more generally Many-body Theory. 

Describe the molecular basis for internal energy, heat transfer, work, and heat capacity. 

Grady and Asay [49] estimate the actual local heating that may occur in shocked 6061-T6 Al. In the work of Hayes and Grady [50], slip planes are assumed to be separated by the characteristic distance d. Plastic deformation in the shock front is assumed to dissipate heat (per unit area) at a constant rate S.QdJt, where AQ is the dissipative component of internal energy change and is the shock risetime. The local slip-band temperature behind the shock front, 7), is obtained as a solution to the heat conduction equation with y as the thermal diffusivity... 

In Chapter 2 we used the laws of thermodynamics to write equations that relate internal energy and entropy to heat and work. 

In this expression consistent units must be used. In the SI system each of the terms in equation 2.1 is expressed in Joules per kilogram (J/kg). In other systems either heat units (e g. cal/g) or mechanical energy units (e.g. erg/g) may be used, dU is a small change in the internal energy which is a property of the system it is therefore a perfect differential. On the other hand, Sq and SW are small quantities of heat and work they are not properties of the system and their values depend on the manner in which the change is effected they are, therefore, not perfect differentials. For a reversible process, however, both Sq and SW can be expressed in terms of properties of the system. For convenience, reference will be made to systems of unit mass and the effects on the surroundings will be disregarded. 

In Chapter 3, we defined a new function, the internal energy U, and noted that it is a thermodynamic property that is, dU is an exact differential. As Q was defined in Equation (3.12) as equal to At/ when no work is done, the heat exchanged in a constant-volume process in which only PdV work is done is also independent of the path. For example, in a given chemical reaction carried out in a closed vessel of fixed volume, the heat absorbed (or evolved) depends only on the nature and condition of the initial reactants and of the final products it does not depend on the mechanism by which the reaction occurs. Therefore, if a catalyst speeds up the reaction by changing the mechanism, it does not affect the heat exchange accompanying the reaction. 

Four Cases Describing How Heat and Work Affect Internal Energy of a System... 

A very important problem in the thermodynamics of deformation of condensed systems is the relationship between heat and work. From Eqs. (2) and (4) by integration, the internal energy and enthalpy can be derived. As in other condensed systems, the enthalpy differs from the internal energy at atmospheric pressure only negligibly, since the internal pressure in condensed systems P > P. Therefore, the work against the atmospheric pressure can be neglected in comparison with the term jX.. Hence it follows that... 

Far more useful are statements that establish the mathematical nature of the internal energy function. Any of the following statements can be considered fully equivalent to the first law, once U is defined in terms of heat and work ... 

Calculate the change in internal energy due to heat and work, Self-Tests 6.2 and 6.3. 

A thermodynamic system (closed system) is one that interacts with the surroundings by exchanging heat and work thru its boundary an isolated system is one that does not interact with the surroundings. The state of a system is determined by the values of its various properties, eg, pressure, volume, internal energy, etc. A system can be composed of a finite number of homogeneous parts, called phases, or there can be a single phase. For some applications, it may... 

Heat and work are forms of energy in transfer between the system and the environment. If more heat is introduced into the system than the system performs work on the environment, the difference is stored as an addition to the internal energy U of the system, a property of its state. In a more abstract way, the first law is said to define the fundamental thermodynamic state property, It, the internal energy. 

Energy can be transferred to (or from) a chemical system from (or to) the surroundings in the form of heat q or work w. The first law of thermodynamics states that the change in the system s internal energy E is equal to the sum of the heat and work inputs (or outputs) ... 

If there is more than one heat or work term, q and w are the net heat and work. E is the total energy of the system—the sum of its overall kinetic and potential energy plus its internal energy. Therefore, we can write... 

We know that the concept of entropy is the fundamental consequence of the second law of thermodynamics. There are two other functions, which utilize entropy in their derivations. These two functions are free energy function and work function. These functions like the internal energy, heat content and entropy are fundamental thermodynamic properties and depend upon the states of the system only. 

It is instructive to outline the thermodynamic argument proving that d= d, g = g, e = e and h = h. The First Law states that the addition of an increment of heat d q to a system produces a change in the internal energy dU and causes the system to do work dW on its surroundings. Thus... 

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