Reaction of a cubic sample

Consider the reaction between a solid A and a gas G, which produces a solid B following  

This reaction is carried out with a cubic sample of A at constant temperature T and the partial pressure P of the gas. The experiments are reproducible and do not present any induction time. 

Enumerate, justifying them, the kind of model (slow or fast nucleation, slow or fast growth) likely to explain the shape of the rate curve. 

Determine the morphologic model (what steps and zone where they occur) of this reactioa Deduce the growth reactivity. 

Give the kinetic curve of the fractional extent versus time for a powder composed of all identical cubic grains with the length of edge 100 om. 

---