We studied At, Kr, CO, and N-2 going into and out of a chemically opened fullerene, 1. We measured the equilibrium constant, K-eq, for the formation of X@1. K-eq is particularly large for Ar, probably due to the large van der Waals attraction between the Ar atom and the fullerene cage. We measured rate constants and activation energies for the unimolecular reaction X@1 -> X + 1 (X = Ar, CO, N-2). The reactions show an unusually small pre-exponential factor, probably due to the loose binding of X inside the cage.