chem confusion :( anode cathode galvanic cells grrrrrr

[physics]

Anna, have you finished the course already?!

who u say finished the course i mean finished summarising only NOT EVEN A QUESTION LPOP only the ones teacher said 2 do

[Edmund]

In Chapter 28, Page 454,:

These are electrolytic cells and not galvanic cells. You may have heard of electrolytic cells as the process of electrolysis (E.g. Water into hydrogen and oxygen). As a results, energy (chemical) is increased.

In Galvanic cells, reactions are spontaneous, where chemical energy is converted into electrical energy though chemical reactions that occur at electrodes. But in Electrolytic cells, reactions are non-spontaneous. This involved having a power source (electrical energy) to produce a chemical change. In other words, the power source forces electrons in the opposite direction compared to the direction in a galvanic cell.

Since electron flow is opposite in electrolytic cells, anode and cathode are reversed - which explains why anode is positive and cathode is negative. It is therefore important to look out for these in the exams - whether it is galvanic or electrolytic.

In the diagram in the on page 454: If this were to be a galvanic cell (no power source, spontaneous reaction), sodium will undergo oxidation and chlorine gas will undergo reduction. But with a power supply, electrons are forced in the opposite direction, making sodium take in electrons (reduction) and Cl^- undergo oxidation.


About the galvanic cell and the salt bridge:

Electrons move from anode to cathode. This makes the anode less negative and the cathode more negative. To balance this charge in both cells, the salt bridge acts to do so. Anions (-) will move to the anode to make it more negative and cations (+) will move to the cathode to make it less negative.

Hope this makes sense...