Question

When hydrochloric acid is added to cobalt nitrate solution at room temperature, the following reaction takes place and the reaction mixture becomes blue. On cooling the mixture, it becomes pink. On the basis of this information mark the correct answer. $\underset{\text{Pink}}{ {[Co(H2O)6]^{3+}}_{(aq)}}$ $+$ ${4Cl^{-}_{(aq)}<=>}$ $\underset{\text{Blue}}{ {[CoCl4]}^{2-}_{(aq)}}$ ${+ 6H2O_{(l)}}$

• A. $\Delta H > 0$ for the reaction
• B. $\Delta H < 0$ for the reaction
• C. $\Delta H = 0$ for the reaction
• D. The sign of $\Delta H$ cannot be predicted on the basis of this information

Answer 1

Answer: (A)

$\Delta H > 0$ for the reaction

Answer 2

$\underset{\text{Pink}}{ {[Co(H2O)6]^{3+}}_{(aq)}}$ $+$ ${4Cl^{-}_{(aq)}<=>}$ $\underset{\text{Blue}}{ {[CoCl4]}^{2-}_{(aq)}}$ ${+ 6H2O_{(l)}}$ On cooling the mixture, the reaction proceeds in backward direction and on heating the mixture, the reaction proceeds in forward direction, hence, the reaction is endothermic i.e., $\Delta H > 0$