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Explain reaction quotient and prediction the direction of the reaction. |
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Answer» Solution :The equilibrium constant of `K_c` and `K_p` helps in predicting the direction in which a given reaction will proceed at any stage. For this, calculate the reaction quotient Q (`Q_c` = molar concentration and `Q_p` = partial pressures). It is DEFINED in the same `Q_c` way as the `K_c` except that the concentrations in `Q_c` are not necessarily equilibrium values. For a general reaction : a A+ b B `hArr` c C + d D `Q_c=([C]^c [D]^d)/([A]^a[B]^b)`=(reaction quotient) (i) If `Q_c gt K_c` , the reaction will proceed in the direction of reactants (reverse reaction). (ii) If `Q_clt K_c` , the reaction will proceed in the direction of the products (forward reaction). (iii) If `Q_c = K_c`, the reaction mixture is ALREADY at equilibrium. The figure given below predict the direction by comparing `Q_c` and `K_c`.  Example : Consider the gaseous reaction of `H_2` with `I_2`. `H_(2(g)) + I_(2(g)) to2HI_((g)) , K_c`= 57.0 at 700K. The molar concentration `[I]_t` = 0.1 M, 112, 0.2 M and `[HI]_2` = 0.40 M the concentrations were MEASURED at some arbitrary TIME t, not necessarily at equilibrium. `Q_c=[HI]^2/([H_2][I_2])=(0.40)^2/((0.1)^2(0.2)^2)=8.0` and `Q_c lt K_c`, So (i) equilibrium is not OCCUR and (ii) Reaction is forward and HI form from `H_2` and `I_2`, So, `Q_c=K_c` . |
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