Thermochemistry

Certain processes that release a great deal of energy are not spontaneous, even though it would seem that they should be. Similarly, certain processes that greatly increase disorder are not spontaneous, although it would seem that they should be. If we mathematically manipulate the expressions for enthalpy and entropy, it is possible to define a new quantity called the Gibbs' free energy. The Gibbs' free energy, sometimes simply called free energy, equals the change in the enthalpy minus the product of the temperature and the change in the entropy. The term free energy should not be misunderstood. As stated earlier, energy can neither be created nor destroyed. This energy does not come free of cost. The term 'free' in "free energy" is better interpreted as available. The free energy can be used to predict if a process is spontaneous or not. If the free energy is negative, the process is spontaneous. If the free energy is positive, the process is not spontaneous. A non-spontaneous process can sometimes be made spontaneous by varying the temperature. If the free energy is zero, the process is at equilibrium, meaning that the forward rate of the reaction equals the reverse rate of the reaction.