Force Majeure refer to unforseeable “superior forces” beyond the control of the contracting parties. Impediment also refers to events beyond the control of the parties. So similar definitions. Both also have the same effect in that neither party need pay damages for non performance due to a force majeure or impediment.
Force Majeure typically refer to events which can not reasonably be anticipated for example Natural Disasters and Acts of War. There are no formal examples of Impediments contained in Article 79 but it would be reasonable to assume that similar examples of Natural Disasters and Acts of War would be regarded as an Impediment.