There are several types of reaction: Combination. Decomposition. Fermentation. Precipitation. Electrolysis. Neutralisation. Redox. Combustion. When a chemical reaction occurs, bonds are broken and then made. Breaking bonds requires energy to be taken in. Bond making releases energy. Bond energy is the energy required to break one mole of bonds, measured in kilojoules. It is also the energy given out when bonds are broken. An exothermic reaction, gives out energy to its surroundings. An endothermic reaction takes in energy from its surroundings. Activation energy is the minimum amount of energy required to start a reaction. The decomposition of a compound by electricity is called electrolysis. Molten ionic compounds are most typically used in electrolysis, since they allow electricity to flow. Positive ions (cations) travel to the cathode (-ve electrode). Negative ions (anions) travel to the anode (+ve electrode). In the electrolysis of solutions the ions in the ionic compound compete with hydrogen ions and hydroxide ions from the water. Electrolysis can be used to deposit metals such as copper, using copper sulphate and copper electrodes. You can use electrolysis to coat one metal with another. This is called electroplating. The chlor-alkali industry uses electrolysis to produce sodium hydroxide, hydrogen and chlorine gas. Brine (sodium chloride solution) is used in this electrolysis. Some reactions never go to completion, they have a forward and a back reaction. These reactions are called reversible reactions. A reversible reaction is in equilibrium when the forward and back reaction proceeds at the same rate.