Whether or not a chemical reaction proceeds in a particular direction depends on a balance between the enthalpy of the system and its entropy.
Gibbs Free Energy allows us to quantify this relationship, and determine whether a particular reaction will be spontaneous.
AUS-e-TUTE members can now access a new tutorial, game, test and exam on this topic.
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There is a "free-to-view" tutorial currently available at http://www.ausetute.com.au/freeenergy.html