The process of intermingling of the ions (molecules) of one substance into another is called:

The process that occurs when ions intermingle in a substance is generally called diffusion. This occurs because of the kinetic energy of ions within the substance that move in random motion. Ions collide and separate resulting into substance to change either from high concentration to low concentration or vice versa.  

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.

500bc indiais the answer.