Application of free energy

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
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 intrrnal energy is the internal energy in the final state,UB minus internal energy in the initial state UA.