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)`

Options

A. `triangleH gt 0` for the reaction
B. `triangleH lt 0` for the reaction
C. `triangleH=0` for the reaction
D. The sign of `triangleH` cannot be predicted on the basis of this information.

Answer

A

Explanation

In the reaction `[Co(H_(2)O))_(6)]^(3+) (aq) +4Cl^(-) (aq) Leftrightarrow [COCl_(4)]^(2-) (aq)+6H_(2)O(l)`
On cooling, the equilibrium shifts backward direction or on heating, the equilibrium shifts forward direction. Hence, reaction is endothermic. i.e. `triangleH gt 0`.