An apparatus that is used to generate electricity from a spontaneous redox reaction or, conversely, that uses electricity to drive a nonspontaneous redox reaction is called an electrochemical cell .
A galvanic (voltaic) cell uses the energy released during a spontaneous redox reaction ( Δ G<0 ΔG<0 ) to generate electricity.
Let’s consider the reaction of metallic zinc with cupric ion (Cu 2 + ) to give copper metal and Zn 2 + ion.
The balanced chemical equation is as follows: Zn(s)+Cu2+(aq) → Zn2+(aq) + Cu(s)
Insert a zinc rod into an aqueous solution of copper(II) sulfate. As the reaction proceeds, the zinc rod dissolves, and a mass of metallic copper forms.
Zinc metal is oxidized to Zn2+ ions at the zinc electrode (the anode), and Cu2+ ions are reduced to Cu metal at the copper electrode (the cathode).
Anode is negative in electrochemical cell because it has a negative potential with respect to the solution while anode is positive in electrolytic cell because it is connected to positive terminal of the battery.