Describe what is meant by dynamic equilibrium.

1. (a)Describe what is meant by dynamic equilibrium.[2]
2. (b)(i)Reaction 4 describes the reversible reaction between yellow Fe3+(aq) and colourless SCN-(aq) to produce red FeSCN2+(aq). reaction 4 Fe3+(aq) + SCN-(aq) ⇌ FeSCN2+(aq) yellow colourless red An equilibrium mixture contains Fe3+(aq), SCN¯(aq) and FeSCN2+(aq). A few colourless crystals of soluble KSCN(s) are added. The mixture is then left until it reaches equilibrium again. The temperature of both equilibrium mixtures is the same. Deduce the changes that occur, if any, in the equilibrium mixture after KSCN(s) is added compared to the original equilibrium mixture. • change in appearance • change in relative concentration of Fe3+(aq) • change in value of the equilibrium constant, Kc[3]
3. (b)(ii)The expression for the equilibrium constant, Kc, for reaction 4 is shown. [FeSCN2+(aq)] Kc = [Fe3+(aq)] × [SCN-(aq)] 5.00 × 10⁻⁵ mol of Fe3+(aq) and 5.00 × 10⁻⁵ mol of SCN-(aq) are added together and allowed to reach equilibrium. The total volume of the mixture is 25.0 cm³. At equilibrium the concentration of FeSCN2+(aq) is 4.23 × 10⁻⁴ mol dm⁻³. Calculate the equilibrium constant, Kc, for reaction 4. Include the units in your answer. Kc = ............................ units ............................[4]
4. (c)Determine the full electronic configuration of Fe3+.[1]
5. (d)SCN-(aq) is colourless. Complete the dot-and-cross diagram in Fig. 3.1 to show the arrangement of outer electrons in an SCN ion. [Figure 3.1][2]

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