Question

When hydrochloric aicd is addded to cobalt and nitrate solution at room temperautre, 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 corect ansewer.
`underset("pink")[[Co(H_(2)O)_(6)]]^(3+)(aq)+4CI^(-)hArr`
`underset("blue")[CoCI_(4)]^(2-)(aq)+6H_(2)O(l)`
A. `DeltaHgt0` for the reaction
B. `DeltaHlt0` for the reaction
C. `DeltaH=0` for the reaction
D. The sign of `DeltaH` cannot be predicted on the basis of this information.

Answer 1

Correct Answer - A
`underset("Pink")([Co(H_(2)O_(6))]_(" "(aq))^(3+))+4Cl_(" "(aq))^(-)hArrunderset("Blue")([CoCl_(4)]_(" "(aq))^(2-))+6H_(2)O_((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., `DeltaHgt0`.