An aqueous solution of blue copper (II) ions can react with chloride ions to form a yellow copper compound. The ionic equation for this reaction is: Cu² + 4CI - ⇌ [CuCl]²-

The forward reaction is endothermic. What two things can you say about the enthalpy change for the reverse reaction?

Since the forward reaction is endothermic (heat is consumed in the reaction) that means that the enthalpy change for the forward reaction is a positive value.

Therefore, i would say that the reverse or backward reaction is exothermic (heat is released in the reaction to the sorroundings) and that the enthalpy change is a negative value.