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      The highly complex organization of living systems requires a constant infusion of ordered energy for development and maintenance. The source of energy is the sun – a giant hydrogen bomb. Green plants the initial trappers of the sun energy, convert solar radiant energy in to chemical energy that is stored in the bonds of organic substances such as glucose. This energy moves through the living world as green plants are eaten by herbivorous animals, which in turn are eaten by carnivorous predators, transformed the energy contained in its meal and creates a store of chemical energy that undergoes continuous transformation at the cellular and sub cellular levels. Because transformations increase the disorder of the energy, some of energy’s capacity to perform useful work is lost from the organisms system in each conversion and must be replaced by new supplies of ordered energy. Thus each link in the food chain passes on less energy than it received from the preceding link. The first low of thermodynamics dictates that the total energy of the products of a reaction will be equal to the total energy of the entering substances; however, the second low indicates that the potential energy of the products will be less than the potential energy of the reactants, i.e. Energy tends to be degraded. In nature, these usually mean that the randomness of any system will tend to increase. Therefore the reaction that is spontaneous may be viewed as downhill events in which entropy increase and energy is released. Thse reactions are classified as exergonic. In contrast, endergonic reactions are uphill reactions in which the randomness of the system decreases. Endergonic reactions can occur only with the input of free energy from an outside source, thus increasing the disorder within that source. Thus the many endergonic reactions occurring in living organisms, which create highly ordered systems, must pay for this order by promoting exergonic reactions as well, such as the catabolism of glucose molecules.





    Kinetic molecular approaches- in this the process is studied in term of atoms and molecules present in the system.Thermodynamics approaches – in this, the process is studied from a consideration of the energy changes involved. The literal meaning of the term thermodynamics is the study of flow heat but actually it deals not only with the relation between heat and work but includes all kinds of interconvertion of one kind of energy into another. Almost all process in nature is accomplished by energy changes. This energy manifests itself in various forms, e.g. Mechanical, electrical, heat, radiation etc. these different forms of energy are interconvertible under suitable conditions and of all forms of energy, heat energy occupies a unique position as all other forms of energy tend to be ultimately converted into heat. The science of thermodynamics attempts to study the laws under living the interconvertiblity of the different forms of energy into heat and to find out the relationship between the different properties of matter which are deducible from these laws.





      The subject matter of thermodynamics is based on three generalizations acquired from human experience with energy. These have been subjected to rigorous mathematical treatment and have yielded logical deduction correlating the various properties of matter. For instance generalization of physical chemistry such as gas equation. Laws of chemical equilibrium. Phase rule distribution laws, Hoff’s laws of dilute solution. Raults laws of vapor pressure lowering and the laws of thermo chemistry can be derived from thermodynamic consideration.


Thermodynamics also provides the basis for forecasting whether certain transformation. Physical an chemical possible or not under a given set of conditions of temperature, pressure, and concentration.






  • While it given the relationship between various properties experimentally observed. It is unable to give them actual values if these properties and does not offer any explanation as to why these properties arise in a system. Where’s, according to kinetic molecular theory, the pressure of a gas is due to the impacts of the molecules on the walls of the vessels and is a measure of these impacts per second. In thermodynamics. Pressure is regarded only as property of the system regardless of its constitution.
  • Another limitation of thermodynamics is in respect of time factor in various transformations. It fails to give any information regarding the time taken for the completion of a change or the rate at which it is brought about.
  • The laws of thermodynamics are based on human experience about the behavior of macroscopic systems i.e. Comparatively large system which are an assemblage of a number of molecules, and hence these laws hold good rigidly.
  • Since human experience is limited to grossly palpable quantities of matter which are fat from being anything on a molecular scale. The deductions of thermodynamics are independent of any hypothesis about the molecular structure of matter.




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