Explain why `cu^(+)` ion is not stable in aqueous solutions?

Explanation

In aqueous solution, `Cu^(+)` ( aq) undergoes disproportionation reaction as follows.
`2Cu^(+)(aq) rarr Cu^(2+) (aq)+Cu(s)`
The higher stability of `Cu^(2+)` (aq) in aqueous solution is due to higher negative enthalpy of hydration `Delta_(hyd)H^(@)` than that of `Cu^(+)`(aq). It compensates the second IE of Cu involved in the formation of `Cu^(2+)` ion. Hence, `Cu^(+)` ion changes to more stable `Cu^(2+)` ion in aqueous medium.