In an electroplating apparatus, where does the reduction reaction occur? a) on the surface of the anode
b) in the solution
c) on the surface of the cathode
d) on the surface of the battery

Spontaneity tell us the direction of the reaction, but not how fast it goes. gibbs free energy brings together enthalpy, entropy and temperature in one easy formula. g = h - ts. and, finally the sign of delta g is always negative for a spontaneous reaction.