Entropy:
Entopy 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,
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.
dictionary defines thermodynamics as"the science of the relations between heat and mechanical work",but it might more usefully be defined as the study of the changes in energy accompanying chemical and physical changes,which allows experimentally determined laws to be derived from certain basic principles,and helps to predict changes which have not been observed.It must be remembered that thermodynamics considers only the initial and final states of any system under going a change,and provides no information about the mechanism of the change between these states,or the rate at which the change takes place-this is the subject of reaction kinetics(where the change taking place is a chemical reaction).
The First Law of Thermodynamics.
This is a law based on experience,and is an extension of the principle of conservation of Energy wich states that energy cannot be created or destroyed,provided that ther is no measurable conversion of mass to energy:it can only be converted from one form to another.The consistency of Joules mechanical equivalent of heat is explained by this principle,and it is clear that if it obeyed,no machine can be devised which will do work without the expenditure of an equivalent amount of energy.In order to metal a given mass of ametal,acertain ammount of energy must be supplied-whether by combustion of afuel or the expenditure of electrical energy.
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.
Theores of reaction .The collision theory.
A perfect theory of chemical kinetics should prvide a method of calculating the rate of any reaction from certain basc principles such atheory has not been produced and there are many difficulites standing in the way of the final calculations in addiation to the complexity of elucidating a basic theory .However we are able to understand certain factors which affect reaction rates and can sometime predict their values with the aid of existing theories.considering ahomogenous bimolecular reaction in he gas phase between two hypothetical molecules a and b it is reeasonable to suppose that.for reaction to occure the molecules a and b must collide.the collision theory of reaction rates due manily to workof w use the kinetick theory of gases to calculate the number of times one molecules of a collides with one of b we will call the total number of colliision per second tacking place between a and b in one cubic centeimetre.then if we assume that each time ,