Question

This question has to do with the reaction Fe3+ + SCN- ---->FeNCS2+

Assume that in a seprate lab exercise, the 3 equilibrium solutions were placed in a water bath and allowed to re-equilibrate at the higher temperature. As a consequence of heating, the Absorbance of the solution was found to decrease. Explain this observation, predict what will happen to the calculated Kc value for this reaction, and determine if the forward reaction is endothermic or exothermic.

Answer 1

Sol:-

The given reaction is :

Fe³⁺ + SCN^- <----------->FeNCS²⁺ + Heat (Exothermic )

With increase in temperature the Absorbance of the solution was found to decrease as a result of which formation of FeNCS²⁺ decreases. Therefore the forward reaction would be exothermic reaction. because according to Le-Chatelier's principle for exothermic reaction with increase in temperature equilibrium shifts in the backward that is in reactant side.

Expression of equilibrium constant i.e k_c is :

k_c = [FeNCS²⁺] / [Fe³⁺] [SCN^- ]

With increase in temperature for exothermic reaction the value of k_c decreases.