F.4 Chem (cell)

In chemical cell, anode=negative electrode ,cathode=positive electrode,but how
about in electrolytic cell?

Remember the rules :
oxidation occurs at anode
reduction occurs at cathode
oxidation-> loss electron
reduction-> gain electron
One problem always occur in studing redox is current =/= electron flow
current, in physics, is classified that : from positive side to negative side.
electron flow : from negative side to postive side
In chemistry, always consider electron flow.
Then you see electron flow from A to B, you should classify A is anode, B is cathode.
. I think you may be confused by "in electrolysis, everything inverse is okay".
In elecytrolysis, you see a battery, ι| , you will classify the long one as positive, and short one as negative, by physics.
But, you find that the +ve side is called as anode, and -ve side called as cathode.
It is because the electron flow is in inverse direction, compared to current.
Electron is still flowing from anode to cathode. You cannot classify as you like.

2.What is the difference between electrolytic cell and chemical cell?
The main difference is electrolytic cell need elect-> electricity.
Electroytic cell has battery while chemical cell not.

But why can't electrolytic cell generates electricity by itself?
In most electrolysis, the reaction in electrolyic cell is always required energy insted of release.
Depends on your purpose, electrolysis threat as separate sth, chemcial cell motivate sth, like battery.

1. When a chemical cell is connected to an external circuit, electron comes out from the negative pole where oxidation takes place while electrons goes back to the cathode which is the positive pole.

The reverse process takes place in the electrolytic cell. Electrons flow from the negative pole of the power supply to the cathode where cations (positive ions) gain electrons. Anions release electrons to the anode which is connected to the positive pole.

In fact, it is meaningless to assign positive and negative poles in an electrolytic cell..

2. As discussed above, in a chemical cell, electrons flow from the anode by chemical oxidation. The electrons do some work in the external circuit e.g. lighting a bulb.This shows conversion of chemical energy to electrical energy then to light energy.

In the electrolytic cell, electropotential energy drives the electrons to the cathode where cations gain electorns and undergo reduction. In this case, the two electrodes can simply be the same (e.g. graphite) and there is no preference for electrons to flow in either direction.Therefore it cannot generate electrical energy itself.

2014-05-23 16:29:24 補充：
CA: you wrote "Electroytic cell has battery while chemical cell not."

It should be re-phrased as "An electrolytic cell needs a battery/cell to work while a chemical cell does not".