the minimum worck

When two components of a solution are mixed ther will be afree energy change and an entropy change involved resulting in either an evolution or an absorption of heat by the system such changes can be measured and can lead to athermodynamic approach to the study of solution such as those in alloy systems,slags and aqueous of solurtions such as those in alloy systems slags and aqueous systems,will cosider the concept of activities in solution and the thermodynamics of solutions which are of fundamental importance to the student of metallurgy whether his interest is in metal extraction corrosion or physical metallurgy.
In the casting of metals the top of the mould can be constructed of substance which evolve heat when they come into contact with a source of heat such as molten metal this evalution of heat by the exothermic materials as they are often called keeps the metal att he top of the casting molten allowing it to feed into the casting and fill the contraction cavity which forms when the metal solidifies one of the reaction tacking place in the exthermic material is the combustion of aluminum powder,the heat change accompanying this reaction is large and negative so that alarge quantity of heat is evolved and the reaction is known as an exothermic reaction hence the name of the materials used in the top of the mould to produce heat.carbon is used to reduce zinc oxide in the commerical extraction of zinc and the reaction can be reperseented, because this reaction absorbs alarge quantity of heat energy the energy is supplied by external heating of the retorts in which the reaction is carrird out with
measurements if they could be made would apparently give us some information about the structure of molecules of solid and liquids but how can this be done what are the entropy unit s mentioned in the , calssical thermodynamics provides the answer in fact historically this approach came before that of statistical thermodynamics the existence of an entropy function was postulated by the thermodynamicists before its behaviour and singnificance were expanded by this statistical mathematicians,in which the system is changed from a to b and back again even though by two different routes we know from the first law of thermodynamic and the nature of thermodynamic variables that the change in intrernal energy will be zero and that values of preasure and volume will not change as a result of asystem being taken through such a cycle.therfore the work done by the system w must be the same as the heat absorbed by the system in traving such a cycle if we have some sort of machine or heat engine which can convert heat into mechanical work we can define the efficiency of the machine which can be converted into work,Electrons have negligible mass compoared with the remainder of the structure and the flow of electricity is not accompanied by a significant movement of matter.Electrolytic coductors contain mobile ions which carry an electrical charge .when an electrical potential is applied these ions will move in the direaction appropriate to their charge.As in electronic conductance the electric current is a movement of electrical charge but this time the charge is carried by ions of significant mass and electrolytic conductance is accompanied by mass transfer conductors may exhibit acombination of electronic and electrolytic conduction but frequently the   proportion of one type is so dominating that it is permissible to assume that the conduction is entirly by the dominating mechanism.This property of electrolytic conduction plays amajor role in some of processes and phenomena important to the metallurgist -corrosion and oxidation of metals, electroplating , electropolishing electrolytic extraction and refining of metas for example,Thermodynamics specifies a "system"as any matter which is being considered which consists of a definite amount of a given substance or substance.The system will have its "surroundings"with which it can exchange energy ,and the system and its surroundings are considered to be isolated they cannot exchange energy with any other system.An example of such asystem would be a steel billet in a reheating furnace-the surroundings of the billet would include not only the structure of the furnace itself,but also the atmosphere inside and outside the furnace,theground on which the furnace stood ,and any other objects which could exchange a measurable amount of energy with the billet , either directly or indirectly.Thus,the First law of thermodynamics states that the total energy of asystem and its surroundings remains constant,evenif it may be changed from one form of energy to another.We can now introduce a quantity U ,which represents the total energy of asystem-whether it be kinetic,electrical,rotational,vibrational,or any other form of energy except the energy due to its position in space,which is assumed to be consta.U is called the internal or intrrinsic energy of the system and is not usually known quantitatively because of the difficulty of measuring all the different forms of energy possesed by actual systems.This is not important because we are concerned with changes in energy ,which can be measured.If the state of a system changes from A to B,for instance as aresult of achange in tempreature,then we say that the change in intrrna