In general, thermodynamics deals with the interconversion of various kinds of energy including heat and the corresponding changes in physical properties.
When applied to chemistry, thermodynamics can be used to predict the extent to which chemical reactions proceed (see also chemical equilibrium).
More specifically, thermochemistry describes three major state functions in a reaction: Entropy (S), Gibb's Free Energy (G) and Heat (H). Entropy is a measure of disorder (and is constantly increasing in the universe), Heat is a measure of the energy of the reaction (not necessarily temperature, which is an average of molecular motion)and Gibb's Free Energy is a measure of work that must go into a reaction to make it occur (when G is negative) or work that a reaction can do (when positive).
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