A spontaneous reaction will always have a negative ΔG (Delta G). This means that the Gibbs free energy of the system decreases, indicating that the reaction proceeds spontaneously in the direction of lower free energy.
ΔH (Delta H) represents the change in enthalpy, or heat content, of the system. A positive ΔH indicates that the reaction is endothermic (absorbs heat), while a negative ΔH indicates that the reaction is exothermic (releases heat).
ΔS (Delta S) represents the change in entropy, or the degree of randomness or disorder, of the system. A positive ΔS indicates that the entropy of the system increases, while a negative ΔS indicates that the entropy decreases.
In summary, for a spontaneous reaction, ΔG is negative and either ΔH or ΔS (or both) could be positive or negative