Can heat energy be transformed into gravitational potential energy? I was wondering it it could be done. I know that Heat is just kinetic energy due to vibration of molecules but is it possible for this transformation of energy?
 A: I'm guessing you're asking how thermal energy makes an object's gravitational field greater. If I've misunderstood you please ignore this answer.
In Newtonian gravity there is no explanation of the fact that the gravitational mass of a body increases as you heat it. You can only understand this by moving to General Relativity. In GR the source of the spacetime curvature, and therefore the gravitational field is an object called the stress-energy tensor. We usually write this as a matrix:

(image from the Wikipedia article linked above)
The top left entry $T^{00}$ corresponds to the mass used in Newtonian gravity, but note that the stress-energy tensor contains extra entries labelled as momentum, shear stress and pressure. Understanding what these mean is a little involved, but see Intuitive understanding of the elements in the stress-energy tensor for an explanation. For now we can skip the details and note that the momentum, shear stress and pressure entries are all associated with exactly the sort of random motion that is caused by thermal energy.
So in summary heating an object makes its component parts (atoms/molecules/whatever) move, and this motion contributes to the entries in the stress-energy tensor and therefore to the spacetime curvature.
