WORLD OF RASAYAN

Introduction Chemical kinetics is the branch of physical chemistry which deals with a study of the speed of chemical reactions. Such studies also enable us to understand the mechanism by which the reactions occur. In chemical equilibria, only the initial and final states were considered, the energy relations between the reactants and the products being governed by thermodynamics where the time or the intermediate states were of no concern. In chemical kinetics the rate of the reaction process is followed; in other words, the time variable is introduced. This, we shall see, reveals not only the influence of different factors on the progress of the reaction but it also throws light on the mechanism through which reactant molecules are transformed into products. It is a common knowledge that apart from the chemical nature, the rates of reaction depend on the concentration of reactants and the temperature. It will be seen later that many reaction rates are greatly influenced by the...

Concept of 'Work' in Thermodynamics

The concepts of heat and work are of fundamental importance in thermodynamics. Work and heat are algebraic quantities and can be positive or negative. They appear only during a change in the state of the system and appear only at the boundary of the system. They are manifestations of energy. Work Work is a basic mode of energy transfer. An object is displaced through a distance dx against a force F(x) then the amount of work which has to be done is defined as W = -F(x)dx In SI System of units, work is expressed in joule or kilojoule; 1J = 1 Nm. When work is done on the system W and when work is done by the system W is negative. There are many types of work and all of them could be expressed as the product of two factors; (i) intensity, and (ii) capacity. Some of these types are: Gravitational work: Gravitational work is said to be done when a body is raised through a certain height against the gravitational field. If a body of mass m is raised through a height h agai...

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