We are being asked to establish an equilibrium reaction. From this equilibrium reaction, we are asked to calculate for the reaction quotient, Q, when solutions are mixed (at time zero).
Furthermore, we are asked to indicate how the reagent concentrations will change as the reaction proceeds.
The concept of Le Chatelier's Principle is applicable to this as all the reactions involved are reversible. Based on this principle, the system will adjust itself in such a way so as to partially offset the stress applied to a system at equilibrium as the system reaches a new equilibrium position.
Below is the step-by-step approach on how this problem is solved:
The chemical equation involved in this equilibrium reaction:
Fe(NO3)3(aq) + KSCN(aq) ⇆ [Fe(SCN)](NO3)2(aq) + KNO3(aq)
Total ionic equation:
Fe3+(aq) + 3NO3- + K+ + SCN-(aq) ⇆ [Fe(SCN)]2+(aq) + 2NO3- + K+(aq) + NO3-
We shall remove spectator ions from the total ionic equation. Spectator ions are those ions that do not contribute or are not involved in the reaction.
When Fe(NO3)3(aq) and KSCN(aq) were initially mixed they reacted and established an equilibrium with [Fe(SCN)]2+(aq). Write the net ionic chemical equation for this reaction. Calculate Q when the solutions are mixed (at time zero). Indicate how the reagent concentrations will change as the reaction proceeds.
Use Le Châtelier's Principle and the “fill in the blank” format provided to explain the effect the added reagent has on the [Fe(SCN)]2+(aq) equilibrium. If a secondary equilibrium is present, support your answer by providing the appropriate balanced net ionic secondary equilibria.
How does the addition of AgNO3(aq) affect the equilibrium position for the reaction? Explain.
The __________ added will react with the free __________ in solution forming ___________ causing the concentration of ______ to __________. The primary equilibrium will shift _________, restoring Keq by replacing the ______________. This shift will result in a(n) _____________ in the concentration of ___________ causing the color intensity of the solution to __________.
Balanced secondary equilibrium: