Equilibrium Constant Expression Equilibrium Constant Expression Many reactions do not proceed even when favorable conditions are maintained. Reactions proceed to some extent and then apparently stop often leaving considerable amounts of unreacted reactants. When such a state is reached in the course of a reaction that no further reaction is apparent, then, it is said to have attained a state of equilibrium at that temperature and the observable properties of the system do not change with time. At this equilibrium the reaction proceeds in both directions at equal rates so that the rate of formations of the products and rate of disappearance of the reactants are exactly equal. Conditions that Affect the Equilibrium :The conditions that affect the equilibrium are According to Le Chatelier’s principle, if a system at equilibrium is disturbed by changing the variables such as pressure, temperature or concentration then the system will tend to adjust itself so as to minimize the effect of that change as far as possible.
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This principle of Le Chatelierâ&#x20AC;&#x2122;s highlights the behavior of a system at equilibrium, if it is subjected to changes in parameters like pressure, temperature, or concentration. Calculating Equilibrium Constant :The ways to calculate the equilibrium constant are <<--- The determination of equilibrium constant requires the equilibrium concentrations or partial pressures of the reactants and the products. <<--- The equilibrium concentrations are determined without affecting the equilibrium state. <<--- Measurements of physical quantities like density, refractive index, light absorption, electrical conductivity etc. may be employed for evaluating the equilibrium concentrations and in such cases the equilibrium state is not affected. Chemical Equilibrium :There are two types of chemical equilibria namely homogeneous equilibria in which all the reactants and products are the same phase and heterogeneous equilibria, where the reactants and the products are present in two or more phases. Chemical Equilibria in Homogeneous Systems 1. Homogeneous reactions in gaseous systems The gaseous reactions are broadly classified into two categories : 1. Gaseous reactions involving no change in the number of moles. 2. Gaseous reactions in which the number of moles of reactants differ from the number of moles of products.
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2. Homogeneous equilibrium in liquid system The principle of Law of Mass action is also applicable to reactions in liquid systems. 1. The equilibrium constant is found to be independent of the volume of the system. 2. Chemical Equilibria in Heterogeneous Systems In heterogeneous systems there are two more phases. In heterogeneous equilibrium, the equilibrium constant involves only the activities or partial pressures of the gaseous constituents and does not include any terms for the concentrations of either pure solids or liquids. By applying law of mass action, and assuming one of the reactants as solid, we could get condensed equilibrium constant equal to the product of partial pressures of the products formed.
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