If an ice cube melts at 0oc but water also freezes at 0oc, what is the difference between melting and freezing in terms of
a. the energy involved in the phase changes and
b. particles of the substances during the phase changes?

The main difference between melting of ice and freezing of water is hydrogen bonds which formed in freezing and broken in melting.

Explanation:

(a) The energy involved in the phase changes:

During melting "energy is absorbed": More hydrogen bonds are being broken as the energy is being absorbed. The molecules are in the solid state and are attraction forces "hydrogen bonds" are high between molecules. The energy absorbed can overcome the attraction between molecules via breaking the hydrogen bonds.During freezing "energy is released": More hydrogen bonds become fixed as energy is being  released. The molecules are in liquid state and when the energy is released the molecules be more attracted and compact via formation of more hydrogen bonds.

(b) Particles of the substances during the phase changes:

During melting "more free to move": Hydrogen bonds get broken and movement can occur. The molecules at first are in solid state "ice" and are bond together. Then, after converting to liquid state after melting, they are more distributed and they move more free than in solid state.During freezing: Hydrogen bonds become fixed and water molecules cannot move as much. In this case, the molecules converted from the liquid state to the solid state, so they be more bond and tightly held. Therefore, the molecules will be in a stationary state and the motion of molecules will not be free.