Cathode/Anode, +/-

[Philip Lee 1L]

The textbook says the following: "A commercial galvanic cell has its cathode marked with a + sign and its anode with a - sign. Think of the + sign as indicating the electrode at which the electrons enter and 'add to' the cell and the - sign as indicating the electrode at which the electrons leave the cell" (7th Edition, pg. 546).

I am a little confused by this statement. I thought that electrons entered the external circuit from the anode (oxidation reaction pushes electrons in) and exited from the cathode (reduction reaction pulls electrons out). Can someone clarify this concept for me?

[Nicolette_Canlian_2L]

since this is a galvanic cell, we know that the reaction occurs spontaneously and energy is not required to start the reaction. You might be mixing this up with the concept of electrolytic cells brought up in lecture today because those require another source of energy for redox reactions to take place.

[Cynthia Aragon 1B]

Voltaic cells are driven by a spontaneous chemical reaction that produces an electric current through an outside circuit which are important because they are the foundation in batteries.
There is a cell that does work on a chemical system by driving an electric current through the system which are called electrolytic cells. Electrolytic cells, like galvanic cells, are composed of two half-cells--one is a reduction half-cell, the other is an oxidation half-cell. The direction of electron flow in electrolytic cells, however, may be reversed from the direction of spontaneous electron flow in galvanic cells, yet the definition of cathode and anode remain the same in which the reduction occurs at the cathode and oxidation occurs at the anode.