Can an equilibrium be reached when there is an excess amount of one reactant over the other reactant? [closed]








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For example, consider a net reaction between ferrous nitrate and potassium thiocyanate:


$$\ce{Fe^3+(aq) + SCN-(aq) <=> (SCN)^2+(aq)}$$


Can an equilibrium be reached if there is a much greater excess amount of one reactant over the other:


$$[\ce{SCN-\_{(aq)}}] \ll [\ce{Fe^3+\_{(aq)}}],$$


or


$$[\ce{SCN-\_{(aq)}}] \gg [\ce{Fe^3+\_{(aq)}}]$$?


If not, is it okay to consider it as an irreversible reaction in these cases?




Whatever the initial and the final amounts of reactants and products, the formation of $\ce{[Fe(SCN)]^{2+}}$ ion is always an equilibrium. If a strong complexing solution, like EDTA, is added to the red solution containing $\ce{[Fe(SCN)]^{2+}}$ ion, whatever the relative amounts of the remaining $\ce{Fe^{3+}}$ and $\ce{SCN-}$ ions, the red color disappears, which means the formation reaction is reversible.


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