Electrochemistry is a particular way of carrying out certain chemical reactions that leads to the production of useful (electrical) work from the free energy of a reaction. Thus, it can be used to produce devices for storage of energy, such as batteries and generation of energy, such as fuel cells. Other applications include industrial production of materials such as aluminum, chlorine and sodium hydroxide, construction of lab instruments, such as pH meters, and in environmental and medicinal chemistry for detecting trace amounts of pollutants in water or specific chemicals in blood, which can signify onset of certain diseases. Thermodynamic arguments will be important for an understanding of electrochemical devices and how useful work is produced by them.