Thermochemistry

Any process that involves a chemical reaction involves change. Sometimes the change occurs on its own. Such a process is called spontaneous. If a change does not occur on its own, it is called non-spontaneous. A spontaneous change may not occur immediately. For example, if a barrel of fuel is left alone, it will remain as fuel indefinitely. However, if a match is used to ignite the fuel, it will burn spontaneously until all the reactants (air, fuel) are completely consumed. In this instance, the spontaneous process required a small amount of energy to be added to the system before a much larger amount of energy could be released. However, once started, it proceeded without assistance. An electrolysis reaction, in which electricity is passed through water to dissociate it into hydrogen and oxygen, is not considered spontaneous because the reaction stops if the electricity is removed. An electrolysis reaction is a non-spontaneous process. How is it possible to determine if a process is spontaneous or non-spontaneous without actually mixing the chemicals together? There are two factors whose combination determines whether a process occurs spontaneously or not. These factors are energy and disorder.