How do you know if a substance can undergo a chemical change?

Change in Temperature
Change in Color
Noticeable Odor (after reaction has begun)
Formation of a Precipitate
Formation of Bubbles

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.

The reaction will shift to the right