Electrochemical Cell EMF | Chemistry Assignment Help
The emf of an electrochemical cell can be measured and can be attributed to the chemical reaction that occurs.
When pairs of electrodes, each likes those electrons which are combined and connected by an external electrical conductor, an electric current flows and chemical reactions occur in the two half cells. Electrodes can be combined without complications if both electrons can operate in the same solution, as in the example of the fig. when this is not tolerated, a connection must be made between the solution that allows ionic conduction to occur between the half cells but prevents mixing of two half cell solutions. A KCl salt bridge, illustrated in the assembly of the fig, is often used. Such a coupling device, indicated by a double vertical line a cell diagram. Has no net influence on the cell reaction. Although some difficulties are introduced into the quantitative interpretation of the cell voltage, or electrochemical force, we set these problems aside for the time being.
The voltage, or emf, of a cell like that of the fig. 2 and 3 can be measured by a voltmeter across the terminals. However, the measured voltage would depend on the current drawn off by the voltmeter. The maximum voltage is that produced in the limit as zero current is drawn. In practice, a suitable value for this characteristic of the cell can be obtained with a vacuum tube voltmeter, which draws a very small current or, more accurately, by a potential arrangement like that shown in fig 3.
In reporting emf results from laboratory measurements, the direction of the electron flow would be given as well as the numerical value of the emf. This direction can be introduced as the diagram of the electrochemical cell by agreeing that the emf will be called positive if there is a tendency for electrons will be accepted by the electrode shown on the left. It is convention that once a diagram of a cell is written, the cell reaction is written so that electrons are accepted from the external circuit by the electrode written on the right and are given up by the external circuit by the electrode on the left.