What reaction (oxidation or reduction) occurs at an anode of...
a) an electrochemical cell
OR
b) an electrolytic cell
What is ALWAYS true. Oxidation ALWAYS occurs at the anode.
In an electrolytic cell the anode is + charged.
In an electrochemicsl cell (a battery or galvanic cell or voltaic cell) the anode is negatively changed.
a) In an electrochemical cell, the reaction that occurs at the anode is oxidation. Oxidation is the process of losing electrons, and it takes place at the anode of the cell. The anode is the electrode where oxidation reactions occur.
b) In an electrolytic cell, the reaction that occurs at the anode is still oxidation. Even though the setup of an electrolytic cell is different from an electrochemical cell, the process of oxidation still takes place at the anode. The anode in an electrolytic cell is still the electrode where oxidation occurs.
To determine the reaction that occurs at the anode of an electrochemical cell or an electrolytic cell, you need to understand a few concepts.
In an electrochemical cell, which is a system that converts chemical energy into electrical energy, oxidation occurs at the anode. Oxidation involves the loss of electrons. Therefore, the anode is where the species being oxidized loses electrons and is subsequently converted into its oxidized form. The cathode, on the other hand, is where reduction occurs, involving the gain of electrons.
In an electrolytic cell, the process is reversed because it relies on the application of an external electrical source to cause a non-spontaneous chemical reaction. In this case, the anode becomes the positive electrode, and the cathode becomes the negative electrode. Hence, at the anode of an electrolytic cell, reduction occurs. Reduction involves the gain of electrons, so the species at the anode will gain electrons and be converted into its reduced form.
To summarize:
a) In an electrochemical cell, oxidation occurs at the anode.
b) In an electrolytic cell, reduction occurs at the anode.
Remember, these definitions are based on the conventional current flow convention, where current is considered to flow from positive to negative.