The significance of the minus sign is that the battery in Fig. 10.8 must supply a voltage in excess of 1.23 V in the indicated sense in order to decompose water into hydrogen and oxygen, both at atmospheric pressure. The overall cell reaction is obtained by summing the anodic and cathodic half-cell reactions shown in Fig. 10.8:
In the anode compartment, water decomposes into: i) oxygen gas, which bubbles off and is collected; ii) hydrogen ions, which migrate towards the cathode in the bridge separating the two compartments; iii) electrons, which enter the external circuit to supply the cathodic reaction. At the cathode, the hydrogen ions and the electrons produced in the anode are combined to produce hydrogen gas.
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Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.