Is Gibbs energy negative?
The change in Gibbs free energy is used to define if a certain reaction takes place spontaneously. You can calculate the change in Gibbs free energy with:
If you have
A negative free energy change
then you calculated the energy remainder, after the spontaneity of the process, that is free to use for other purposes.
A positive free energy change
then you calculated the minimum amount of energy needed to run the process spontaneously.