Conversion of work to heat

Mayer was trained as a medical doctor and was a ship-surgeon on a vessel trading to the East Indies. His first ideas about the conversion of work to heat came from his observation of the difference in venous blood color between the tropics and higher latitudes. He concluded that in the warm... 

Describe one of Joule s experiments for the conversion of work to heat, and - using what you consider reasonable data - calculate the obtained temperature increase. Any comments on the required accuracy ... 

Heat, like work, is energy in transit and is not a function of the state of a system. Heat and work are interconvertible. A steam engine is an example of a machine designed to convert heat into work.h The turning of a paddle wheel in a tank of water to produce heat from friction represents the reverse process, the conversion of work into heat. 

What about points to the right of 2 Can they be reached Consider an adiabatic path from point 1 to point 2a that is also located on the isothermal Qj. The cycle of interest is 1 — 2a —> 2 — 1. Again, two of the three steps are adiabatic. In this case, however, heat is evolved during the 2a —> 2 step from the conversion of work into heat. The complete conversion of work into heat is a well-known phenomenon and is not forbidden by the laws of thermodynamics. Thus, there are states to the right of 2 on the isotherm O2 that are accessible from 1 via an adiabatic path. 

This assumes that the engine is reversible. If it were a real engine and operated at a finite speed, due to friction, we would have actually achieved a conversion of work into heat. 

A coil of wire wound round an iron core was made to rotate in a calorimeter between the poles of a horse-shoe magnet. Electric currents are produced in the wire, and are in turn converted into heat owing to the electrical resistance of the coil. The conversion of work into heat takes place indirectly by means of the electric current. By this method Joule obtained the mean value J = 459-62 kgm. for the mechanical equivalent of heat. 

One of the possible reasons why the question of rheological vs. interfacial mechanisms of interaction has been so difficult is that another mechanism has been neglected. The process involved in this mechanism is the conversion of work into heat.(i 3) We will examine this process in the fourth section of this chapter. In the main body of the chapter, we will develop an isothermal theory in a way that will enable us to introduce thermal effects in Section 4. 

An energy conversion cyclic system that converts heat to work, and sometimes work to heat, is the foremost objective of thermodynamics. 

The second law does not prohibit the production of work from heat, but does place a limit oq. the fraction of the heat that may be converted to work i any cyclic process. The partial conversion of heat into work is the basis for nearly all commercial production of power (water power is an exception). The develop ment of a quantitative expression for the efficiency of this conversion is the nex step in the treatment of the second law. 

The first evidence for cobalamin involvement in the conversion of methanol to methane was provided by Blaylock and Stadtman [196,216-218] with extracts of methanol-grown M. barkeri they demonstrated enzymatic formation of methylcobalamin from methanol, and subsequent reduction of methylcobalamin to methane. Later Blaylock [196] showed that conversion of methanol to methylcobalamin requires a heat-stable cofactor and at least three proteins, a 100-200 kDa Bi2-enzyme (methyltransferase), a ferredoxin, and an unidentified protein. Blaylock speculated that the role of hydrogen and ferredoxin in the conversion of methanol to methylcobalamin was in the reduction of the Bi2-protein. This work led to the proposal that methylcobalamin was the direct precursor of methane in methanogenesis from various substrates [196,218]. 

The work of Blaylock and Stadtman has significantly advanced our knowledge of the conversion of methanol to methane in Methanosarcina, A system has been developed in which Bi2s serves as the methyl acceptor in the enzymic activation of methanol. These studies have revealed an unexpected complexity of this methyl transfer reaction the requirements include ferredoxin, a corrinoid protein, an unidentified protein, ATP, Mg, a hydrogen atmosphere, and a heat-stable cofactor for the transfer of the methyl group of methanol to Biog (12). 

A similar lack of clarity pervades other areas concerning the relationship between the catalytic performance and fundamental properties of the catalysts. Wakabayashl et al. (10) reported that the optimized conversion of propylene to acrolein (>7%) over alumina-supported tin-antimony oxide (3 1) was dependent on the sintering temperature of the catalyst and was maximized after heating at 10(X)°C for 3 hr. Further work (22) showed that both electrical conductivity and surface area were maximized in the material containing 3% antimony and a close association between acrolein production and solid solution formation was suggested. 

An alternative wording of the Kelvin-Planck statement is that heat cannot be completely converted to work in a cyclic process. However, it is possible, as shown above, to do the converse and completely conven work to heat. Since heat cannot be completely converted to work, heat is sometimes considered a less useful form of energy than work. When work or mechanical energy is converted to heat, for example, by friction, it is said to be degraded. 

---