The analytic calculations of relaxation length of electron energy based on a probabilistic approachand numerical calculations of nonlocality effect on the plasma-chemical processes rates have been carriedout for plasma of an electronegative glow discharge in a mixture of xenon and chlorine. It is shown, that for total pressure higher than 6 Torr and with amount of chlorine more than 1/25 the effect of electronenergy distribution nonlocality is negligibly small and the local approach can be used for modeling such discharges.