Aqueous iron(Ill) ions can be represented as [Fe(H_2O)_6]^3+(aq) to explicitly e

Question

Aqueous iron(Ill) ions can be represented as [Fe(H_2O)_6]^3+(aq) to explicitly emphasize the six particular water molecules in close contact with the ion. From this perspective, the formation of the thiocyanatoiron(III) iron can be understood as thiocyanate replacing one of these six water molecules. [Fe(H_2O)_6]^3+(aq) + SCN^-(aq) [Fe(H_2O)_5SCN]^2+(aq) + H_2O(l) Based on the observed premature dependence of the equilibrium constant and what that implies about Delta H, what can be inferred about the relative strength of the Fe^3+ -H_2O interaction and the Fe^3+ -SCN^- interaction?

Explanation / Answer

Equilibrium constant of any equilibrium depends on temperature. Thus, if the reaction is exothermic, then equilibrium constant will decrease with increase in temperature. Similarly, for an endothermic reaction, equilibrium constant will increase with increase in temperature. Here, the equilibrium constant is increasing with increasing temperature. This shows that the reaction is endothermic and heat is absorbed during the reaction. This also indicates that the enthalpy of formation of the product is less than the enthalpy of formation of reactants. Here, in the provided example, Fe-OH2 interaction is stronger than the Fe-SCN interaction and if the interaction is stronger, it will have higher enthalpy of formation also.

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