Question

Given the following equilibrium reaction: Fe3+(aq) + 4CN-(aq) <--> Fe(CN)64-(aq)If the equilibrium constant, Kc, is equal to 1.2 x 10^10 at 25°C, what will be the value of Kc at 50°C? And how will the equilibrium position shift when the temperature is changed from 25°C to 50°C?

Answer 1

To determine the value of Kc at 50C, we need to know the enthalpy change  H  of the reaction and use the van't Hoff equation:ln K2/K1  = -H/R *  1/T2 - 1/T1 where K1 is the equilibrium constant at temperature T1  25C , K2 is the equilibrium constant at temperature T2  50C , R is the gas constant  8.314 J/molK , and H is the enthalpy change of the reaction.Unfortunately, without the value of H, we cannot calculate the exact value of Kc at 50C.However, we can still discuss how the equilibrium position will shift when the temperature is changed from 25C to 50C. If the reaction is exothermic  H < 0 , increasing the temperature will shift the equilibrium position to the left, favoring the reactants. If the reaction is endothermic  H > 0 , increasing the temperature will shift the equilibrium position to the right, favoring the products.