Is Gibbs free energy the sole determiner for spontaneity?

If a reaction has negative $\Delta G$, can we then say with *certainty* that the reaction will be spontaneous?


Is negative $\Delta G$ the sole determinant for spontaneity?




For a spontaneous process at ***constant temperature and pressure***, $\Delta G$ ***must*** (emphasis on must) be negative. 


Spontaneity of a process , explicitly, depends on the enthalpy change and the entropy change. The Gibbs free energy change includes both these factors to predict the spontaneity of a process.


So, yes it can be said that Gibbs free energy change is the main factor that decides the spontaneity of a process.


Putting into better words, $\Delta G$ being negative is a consequence of a process being spontaneous.


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