Driving force
When the structure of a material changes there has to be a driving force
The fact that a driving force exists does not mean that the reaction will take place - kinetics is an issue
When a material system is out of equilibrium and changing spontaneously there is a one way movement of atoms from one place to another
In principle this systematic flow can be harnessed to do mechanical work (c.f. pushing pistons in an engine)
At equilibrium the system can no longer do work as there is no net flow of particles
A chemical change thus goes in the direction where it can release energy as work