We know that according to Le Chateliers principle that an increase in temperatur

Question

We know that according to Le Chateliers principle that an increase in temperature causes the endothermie reaction to occur in our cobalt system. Based on the color changes you see, is this statement supported for the cobalt complex ion system? Explain. Would the value for K (the equilibrium constant) increase, decrease or stay the same for this reaction if heat were applied? Explain. Is this a reversible reaction? If so, is the reverse reaction for the equation given on page 76 endothermie or exothermic?

Explanation / Answer

(1) Since DH > 0 => forward reaction is endothermic and heat is absorbed

[Co(H2O)6]2+(aq) + 4 Cl-(aq) + heat <=> [CoCl4]2-(aq) + 6 H2O(l)

As temperature increases => heat is added

=> equilibrium shifts to right (endothermic reaction occurs) according to Le Chatelier's principle

=> [Co(H2O)6]2+ is converted into [CoCl4]2-

=> color changes from pink (excess [Co(H2O)6]2+) to violet (mixture of [Co(H2O)6]2+ and [CoCl4]2-) to blue (excess [CoCl4]2-)

=> Yes, the statement is supported for the cobalt complex system

(2) From van't Hoff equation:

ln(K2/K1) = (-DH/R) x (1/T2 - 1/T1)

For an endothermic reaction, DH > 0

=> K2 > K1 when T2 > T1

=> equilibrium constant K increases if heat is applied and temperature increases

(3) Yes, the reaction is reversible.

Since the forward reaction is endothermic (absorbs heat)

=> the reverse reaction is exothermic (releases heat)

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