We probably need a chemist or physicist to answer that.
But since I'm at it, I'll give ity a shot
When you say "change in size" do you mean an increase in the volume they occupy in space?
Or do you mean an increase in mass (ie. a chemical reaction that would add more atoms to that molecule) ?
If you mean the volume then yes, it would increase in volume for the reasons listed above (and maybe other reasons unknown to me
).
If you mean increase in mass, I believe you need either a chemical reaction or a means to accelerate the mass in question to a VERY fast speed (the closer to the speed of light, the better).
Don't think I can contribute at any higher level, chemistry in not my thing.
palgia
PS. Just out of curiosity, are you asking out of personal interest or are you trying to apply this to some practical application (ie. answer the ATPL MET questions) ?