The Conversion of Work to Heat

This idea, as expected, generated tremendous opposition because it was contrary to the doctrine of the conservation of heat that was deeply rooted as the basis of the science of heat at that time. Its establishment belongs to Julius Robert Mayer and, especially, to James Prescott Joule. 

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 

To determine the equivalence between heat and work Mayer relied on the difference in gas heat capacities at constant pressure and at constant volume. In the case of the constant pressure heat capacity Cp, the amount of added heat not only raises the temperature of the gas, but also must account for the work of expansion of the gas against the external pressure. This work is not, of course, involved in the constant volume heat capacity Cy, and thus Cp is larger than Cy. Arguing that all the extra heat was converted to work, he arrived at the number of 356 kg.m per kilocalorie (664.8 ftlbf/Btu), about 15% less than the accepted value today. 

Mayer published his findings in 1842, but his ideas were not accepted First, he did not prove that all the extra heat (for Cp) was used for work against the external pressure. 

Second, the idea of a loss of caloric (heat) by conversion to work was against the aforementioned conservation of heat axiom. 

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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. 

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. 

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. 

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). 

The present world rcscr es of natural gas that contains mainly methane are still underutilized due to high cost of transportation. Considerable interest is therefore presently shown in the conversion of methane to transportable liquids and feedstocks in addition to its previous sole use for heating purposes by combustion. One possible new route for the utilization of methane derived from natural gas or other sources for conversion to more valuable higher hydrocarbons is the methylation of aromatic hydrocarbons. This chapter provides a general overview of the work that has been done so far on the use of methane for catalytic methylation of model aromatic compounds and for direct liquefaction of coal for the production of liquid hydrocarbons. The review is especially focused on the use of both acidic and basic zeolites in acid-catalyzed and base-catalyzed methylation reactions, respectively. The base-catalyzed methylation reaction covered in this discussion is mainly the oxidative methylation of toluene to produce ethylbenzene and styrene. This reaction has been found to occur over basic sites incorporated into zeolites by chemical modification or by changing the electronegative charge of the zeolite framework. 

Heat inactivates enzymes, so when fresh corn is immediately plunged into boiling water, the conversion of sugar to starch is arrested. This aspect of com chemistry presents a real problem when it comes to freezing cobs. In a frozen state, the enzymes keep working — albeit much more slowly — and this leads not only to sugar loss but also to the destraction of some of corn s flavor compounds. So, we have to blanch corn before freezing it. 

Herve Clavier and Steven P. Nolan, now at St. Andrew s University, found (Adv. Synth. Cat. 2008, 550, 2959) that the indenylidene Ru complex 1 was an excellent pre-catalyst for alkene metathesis. A combination of 1 and the ligand 2 effected cross metathesis of 3 and 4 in just 15 minutes under microwave heating. Robert H. Grubbs of Caltech designed Organic Lett. 2008, i 0, 2693) the Ru catalyst 6 for the preparation of tri- and tetrasubsti-tuted alkenes, as illustrated by the conversion of 7 to 8. The catalyst 6 also worked well for cross metathesis and ring opening metathesis pol nnerization (ROMP). 

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