Surface free energy, being an intensive property, does not vary with volume. We then consider a small change in shape for a constant volume. If a crystal were nucleated to a thermodynamically unstable state, then the change it would undergo afterward to approach an equilibrium shape would be under the condition of constant volume. By definition of holding a variable constant, the change must be zero, δ δ ( V c ) V c = 0 . Then by expanding V c in terms of the surface areas O j and heights h j of the crystal faces, one obtains