Question

1. how can Kc of the two possible reactions be compared to determine which reaction occurring?

2. how are the equilibrium moles of reactants (ions remaining in solution) calculated?

3. what are the equilibrium constant equations for the below reactions?
Fe3+ + SCN- <---> FeSCN2+

Fe3+ + 2SCN- <--->Fe(SCN)2 +

Answer 1

1) When we know the numerical value of the equilibrium constant, we can make certain judgments about the extent of the chemical reaction.

K > 1

If K is larger than 1, the mixture contains mostly products.

K < 1

If K is less than 1, the mixture contains mostly reactants.

K = 1

If K is about equal to 1, the reaction will reach equilibrium as an intermediate mixture, meaning the amounts of products and reactants will be about the same.

2) $aA+bB⇌cC+dD$

$K = \dfrac{(a_C)^{c}(a_D)^{d}}{(a_A)^{a}(a_B)^{b}}$

3) $Fe^{3+} + SCN^- <-> FeSCN^{2+}$

$K=\frac{[FeSCN^{2+}]}{[Fe^{3+}][SCN^-]}$

$Fe^{3+} + 2SCN^- <->Fe(SCN)_2^ +$

$K=\frac{[FeSCN^{2+}]}{[Fe^{3+}][SCN^-]^2}$