What is a reaction with a negative #DeltaG# and occurs spontaneously?
What, an example? Because all reactions with
#2"Al"(s) + 6"HCl"(l) -> 2"AlCl"_3(aq) + 3"H"_2(g)#
As you form a gas and an aqueous solution from a solid and a concentrated aqueous solution, you increase the entropy of the system after the reaction (because gases move around much more than liquids and solids).
#color(green)(DeltaS_"rxn" > 0)#.
Furthermore, this reaction is known to release heat (you may or may not do it in lab someday), so
#DeltaG = DeltaH - TDeltaS#
#DeltaG = (-) - T(+)#