Final answer:
The anode is negatively charged in an electrochemical cell due to spontaneous oxidation, while in an electrolytic cell, it is positive because an external power source drives oxidation. The cathode is positive in an electrochemical cell as it receives electrons, and negative in an electrolytic cell where it is connected to the negative terminal.
Step-by-step explanation:
Understanding the nature of anodes and cathodes in different types of cells is a crucial part of electrochemistry. In an electrochemical cell, which includes galvanic and voltaic cells, chemical energy is converted into electrical energy through spontaneous redox reactions. In such cells, the anode is considered the negative electrode because this is where oxidation occurs and electrons are produced - these electrons then flow through the external circuit to the cathode, which is the positive electrode and the site of reduction.
Conversely, in an electrolytic cell, electrical energy is used to drive nonspontaneous chemical reactions. Here, the anode is connected to the positive terminal of the external battery or power source, making it the positive electrode, as it still is the site of oxidation but requires energy input to proceed. The cathode in this case is negative because it is connected to the negative terminal of the power source and is where reduction and gain of electrons occur.
This difference lies in the direction of electron flow driven by the cell's function: in the electrochemical cell, the anode 'pushes' electrons out due to spontaneous reaction, while in the electrolytic cell, the external power source 'pulls' electrons into the anode. In both cases, however, the fundamental processes of oxidation at the anode and reduction at the cathode remain consistent.