The master equation of a chemical model for the Lorenz equations was examined by ensemble simulations in this paper. It was found chat, due to the East separation of nearby simulation runs, the representative points in the ensemble which initially assembled densely in the concentration phase space fell apart and extended to distribute on the overall chaotic attractor. Results revealed that intrinsic fluctuations in systems of deterministic chemical chaos are very large and the ensemble-averaged values of concentration are therefore meaningless. Nevertheless, the structure and dynamics of individual simulation runs, which are numerical realizations of the underlying jump Markov process, are in good coincidence with the deterministic chaotic attractor.