Electrochemical Cells
- These are systems consisting of electrodes that dip into an electrolyte.
- There are two electrodes which represent the two half reactions in a redox reaction.
- This chemical reaction (redox) either uses or produces electricity (a flow of electrons).
1. Voltaic Cell – an electrochemical cell in which a spontaneous reaction generates an electric current which is measured in volts.
2. Electrolytic Cell – an electrochemical cell in which an outside electric current drives an otherwise non-spontaneous reaction.
1. Voltaic Cell
- Consists of two half-cells – a metal strip (an electrode) that dips into a solution of its metal ion.
- A voltaic cell is connected to a volt meter which measures the electricity produced.
- The electron flow From Anode To CAThode. (FAT CAT)
- ANO (anode, negatively charged, oxidation)
- CPR (cathode, positively charged, reduction)
- Salt bridges – a tube of electrolyte (ionic compound) in a gel that is connected to the two half-cells.
- The electrolyte (usually KCl) will carry electrons in the voltaic cell.
- The ions in the electrolyte can move through the gel and into the half-cells. This prevents build-up of either a positive or negative charge.
- A shorthand means of writing what happens in a voltaic cell is called ‘cell notation’
Zn(s) | Zn2+(aq) || Cu2+(aq) | Cu(s)
Key parts of the notation are
- The components of the anode compartment (oxidation half-cell) are written to the left of the components of the cathode compartment (reduction half-cell).
- A vertical line represents a phase boundary. A comma separates half-cell components in the same phase. Often, we specify the concentrations of dissolved components.
- Half-cell components usually appear in the same order as in the half reaction, and electrodes appear at the far left and right of the notation.
- A double vertical line separates the half cells and represents the phase boundary on either side of the salt bridge (the ions in the salt bridge are omitted because they are not part of the reaction).