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Explain the use of equilibrium constant to predicate the proportion of reaction with example. |
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Answer» Solution :The numerical value of the equilibrium constant for `(K_c)` a reaction indicates the extent of the reaction but equilibrium constant does not give any information about the rate. The magnitude of `K_c` or `K_p` is directly proportional to the concentrations of products and inversely proportional to the concentrations of the reactants. "As the value of K is high the concentration of product remain high and as the value of K is low the concentration of the products remain low. Value of K `PROP` [Products] `prop 1/"[Reactants]"` The following generalisation covering the composition of equilibrium MIXTURES. (a)If `K_c gt 10^3` : Products predominate over reactants, i.e., if `K_c` is very large, the reaction proceeds nearly to completion. Consider the following examples : (i) The reaction`H_2+1/2O_2 to H_2O` of `H_2` with `O_2` at 500 K has a very large equilibrium constant `K_c`. `K_c=2.4xx10^47` (ii)`H_(2(G)) + Cl_(2(g)) hArr 2HCl_((g))` at 300 K has a very large `K_c`. `K_c=4.0xx10^31` (iii)`H_(2(g)) + Br_(2(g)) hArr 2HBr_((g))` at 300 K has a very large `K_c`. `K_c=5.4xx10^(18)` (b) If `K_c lt 10^(-3)`: Reactants predominate over products, i.e., if `K_c` is very small, the reaction proceeds rarely. Consider the following examples (1) The decomposition of `H_2O` into `H_2` and `O_2` at 500K has a very small equilibrium constant `K_c=4.1xx10^(-48)` (ii) At 298 K temp, inatmosphere `N_2` and `O_2` combine as `N_(2(g)) + O_(2(g)) hArr 2NO_((g))` the `K_c=4.8xx10^(-31)` is very less. (c) if `K_c` is in the range of `10^(-3)` to `10^(+3)` : Appreciable concentrations of both reactants and products are present. Example : The value of K is important for the following reaction. (i) For reaction of `H_2` with `I_2` to give HI, `K_c` = 57.0 at 700 K. (ii) Gas phase decomposition of `N_2O_4` to `NO_2` is another reaction with a value of `K_c = 4.64 xx 10^(-3)` at `25^@C` which is neither too small nor too large. Hence, equilibrium mixtures contain appreciable concentrations of both `N_2O_4` and `NO_2`. The values of `K_c` and the ratio of reactants and products at the equilibrium can show by the figure GIVEN under: 
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