A positive enthalpy of formation indicates that energy has to be provided in order for the reaction to proceed. A negative enthalpy of formation indicates that energy is evolved. What the enthalpy of formation tells us is the change of enthalpy that would occur if a reaction pathway could be found that takes one of the elements to the compund of interest. Entropy The entropy, S, of a system is a measure of its randomness or, its disorder. This increase in entropy arises because the reaction releases energy into the surroundings.
All endothermic reactions decrease the entropy of the sorroundings.
This large positive quantity indicates that the reaction is spontaneous and a thermodynamic reason why steel corrodes. Because this is a small, negative value, we can conclude that this reaction does not go to completion. Gibbs Free Energy. When a reversible chemical change occurs, the difference between H and T S represents the amount of available energy released or absorbed as a result of the chemical change. This energy represents the driving force of the reaction.