chem!(urgent!!!!)

如果你係中四/中五，請打開你本書有關Simple chemical cell個課=\/=
An electrochemical cell is a device used for creating an electromotive force (voltage) and current from chemical reactions. The current is caused by the reactions releasing and accepting electrons at the different ends of a conductor.
In each half-cell is a chemical undergoing either oxidation or reduction. In a full electrochemical cell, one side must be losing electrons (oxidation) to its electrode while the other half-cell gains electrons (reduction). If the atoms/ions involved in the reaction are metal, the same metal is used for each electrode. If the atoms/ions involved in the reaction at each half-cell are not metal, no electrode can be constructed out of it. Nonreactive metals such as platinum are used as a substitute (as in the standard hydrogen electrode). Finally, a salt bridge is necessary to provide electrical contact between the cells—but without the solutions mixing. This can simply be a strip of filter paper soaked in saturated potassium nitrate (V) solution.

圖片參考：http://upload.wikimedia.org/wikipedia/en/thumb/3/39/ElectrochemCell.png/250px-ElectrochemCell.png


2007-04-18 09:03:59 補充：
Example:A simple chemical call with Zn electrode, Cu electrode and dil. H2SO4 as electrolyte.since Zn is more ready to give electrons than Cu, electrons flow from Zn to Cu. Electrons carry electrical energy. Therefore a voltage is produced.

2007-04-18 09:04:13 補充：
At Zn electrode(anode): Zn ---> Zn2+ + 2e-At Cu electrode(cathode): 2H+ + 2e- ---> H2Overall equation: Zn + 2H+ ---> Zn2+ + H2