It will depend on the composition of the blocks. Since the system is isolated, the entropy change is zero. In thermal equilibrium, the system is more ordered, so the entropy change is negative. Since the heat flow is irreversible, the entropy change is positive. Gases and liquids tend to take the shape of their containers, but solids do not.
Liquids are generally much more compressible than solids.
A liquid will expand to fill a closed container, while a gas will not. The molecules in a liquid are rigidly held in place. None of these. An atom is the smallest bit of an element that has all the chemical properties of that element. A compound is a combination of elements.