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Cobalt complexes and hydrogen iodide

Kc, Q, Le Chatelier with observations, collision theory

**System 1:** [Co(HX2O)X6]X2+(aq)+4 ClX−(aq)⇌[CoClX4]X2−(aq)+6 HX2O(l)\ce{[Co(H2O)6]^2+(aq) + 4Cl-(aq) <=> [CoCl4]^2-(aq) + 6H2O(l)}; ΔH>0\Delta H > 0. [Co(HX2O)X6]X2+\ce{[Co(H2O)6]^2+} is pink; [CoClX4]X2−\ce{[CoCl4]^2-} is blue. **System 2:** HX2(g)+IX2(g)⇌2 HI(g)\ce{H2(g) + I2(g) <=> 2HI(g)} at 450 °C. IX2(g)\ce{I2(g)} is purple; HX2\ce{H2} and HI are colourless.
Facts you may need
  • Kc expressions (no water or solids)
  • Le Chatelier's principle
  • activation energy and collision theory

(a)

Write the KcK_c expression for System 1. Predict and explain the observations when (i) the mixture is heated, (ii) water is added, (iii) a few drops of AgNOX3(aq)\ce{AgNO3(aq)} are added.

(b)

0.200 mol of HX2\ce{H2} and 0.200 mol of IX2\ce{I2} are sealed in a 2.00 L flask at 450 °C. At equilibrium [HI]=0.156[\ce{HI}] = 0.156 mol L−1^{-1}. Calculate KcK_c.

(c)

Another mixture at 450 °C contains [HX2]=[IX2]=0.050[\ce{H2}] = [\ce{I2}] = 0.050 and [HI]=0.50[\ce{HI}] = 0.50 mol L−1^{-1}. Determine whether it is at equilibrium, and describe the colour change as it moves towards equilibrium.

(d)

State and explain the effect of (i) adding a catalyst and (ii) raising the temperature on the RATE of System 2 and on the value of KcK_c. (ΔH\Delta H for System 2 is small and negative.)